Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

2014-05-02 17:23 GMT+02:00 Pieren :

> On Fri, May 2, 2014 at 4:41 PM, John F. Eldredge 
> wrote:
> > Layer = -1 is not valid data for a waterway that is on the surface,
> which by definition is layer 0. It is only valid data on an underground
> waterway.
>
> Pfff, Martin, why did you restart this thread ?
>


sorry, came back from holidays and didn't see that is was already a week
old. ;-)



> Water is always below the ground, otherwise it's a flood ;-)



nope, waterways are almost always on the ground  (surface water, french:
eaux superficielles), otherwise it is groundwater (french eau souterraine).
Rivers, streams, canals etc. are generally surface water.

Anyway, this has nothing to do with the layer tag. I believe it was already
said ~5 times this year on this list, but some repetition won't harm:
if no explicit layer tag is set an object is supposed to be on layer=0, but
this has nothing to do with underground vs. on the ground. The layer tags
define stacking locally, i.e. when several objects overlap (in 2D) a
different layer tag indicates that this is not happening in the same layer,
but that one object is above the other, the higher the layer number the
higher the object. Objects at the same spot on the same layer do
intersect/overlap.

This has also nothing to do with tagging for the rendering, it is a rough
representation of 3-dimensional objects in a 2,5D space. When rendering you
can use the layers as rendering order, but you do not have to, often you
will decide to draw lower features above higher ones in order to make them
visible.

cheers,
Martin
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Pieren]

On Fri, May 2, 2014 at 4:41 PM, John F. Eldredge  wrote:
> Layer = -1 is not valid data for a waterway that is on the surface, which by 
> definition is layer 0. It is only valid data on an underground waterway.

Pfff, Martin, why did you restart this thread ?
Water is always below the ground, otherwise it's a flood ;-)

Pieren

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[John F. Eldredge]

Layer = -1 is not valid data for a waterway that is on the surface, which by 
definition is layer 0. It is only valid data on an underground waterway.


On May 2, 2014 7:16:04 AM CDT, Martin Koppenhoefer  
wrote:
> 2014-04-24 0:52 GMT+02:00 Bryce Nesbitt :
> 
> > If one could simply delete the layer=-1 on a waterway, without
> getting
> > yelled at by validators, then human effort could be directed to
> those true
> > oddball situations (like canals crossing each other) that really
> need
> > detailed tagging.
> 
> 
> 
> why would you want to remove valid detail? Even if it seems redundant
> at
> first glance still it is a kind of confirmation and therefor better
> than an
> implicit default (IMHO).
> 
> cheers,
> Martin
> 
> 
> 
> 
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"Darkness cannot drive out darkness; only light can do that.  Hate cannot drive 
out hate; only love can do that."
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

2014-04-24 0:52 GMT+02:00 Bryce Nesbitt :

> If one could simply delete the layer=-1 on a waterway, without getting
> yelled at by validators, then human effort could be directed to those true
> oddball situations (like canals crossing each other) that really need
> detailed tagging.



why would you want to remove valid detail? Even if it seems redundant at
first glance still it is a kind of confirmation and therefor better than an
implicit default (IMHO).

cheers,
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Bryce Nesbitt]

>
> the problem has more causes. But mainly people got used to use the
> layer=-1 as
> a cheap trick to hide all kinds of pesky keepright/JOSM warnings about
> missing
> bridges, incorrect crossings, waterway crossing waterway and a few more.
> The problem would also go away if validators would detect this abuse.
>

I see the *core* of the problem as validator warnings about crossings of
rivers and ways.  That goes for JOSM and KeepRight at least.

There's a sensible default assumption (the waterway is culverted under the
way) that serves pretty darn well.

If one could simply delete the layer=-1 on a waterway, without getting
yelled at by validators, then human effort could be directed to those true
oddball situations (like canals crossing each other) that really need
detailed tagging.

---
Thus the proposal: swap the validator warning about way crossing, with one
about inappropriate use of level.
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Tue, 22 Apr 2014, Richard Z. wrote:

> On Tue, Apr 22, 2014 at 10:54:37PM +0300, Ilpo Järvinen wrote:
> > On Tue, 22 Apr 2014, Richard Z. wrote:
>  
> > > Now what is that key:layer anyway? Given that nobody knows or cares how 
> > > it 
> > > works does it do more good than harm? Do we need it at all?
> > > Or should we make a fresh start with something well defined and deprecate
> > > this mess?
> > 
> > I personally think that only thing that would need to be added/defined, is 
> > sensible defaults for bridges/tunnels (less weight than layer=*) and get 
> > "validators" updated. For some yet to be explained reasons, some people 
> > spread FUD about that being impossible but it's clearly incorrect claim
> > if the implicit default is correctly defined.
> 
> that might actually work, but what is the advantage over a JOSM preset
> with a layer=1 as default?

I don't know about you, but I've never used a preset to add a bridge
It's just adding a single tag which is likely around magnitude faster with 
keyboard than navigating zillions of presets, providing "input" to the 
preset, etc. ...That means the problem remains.


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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Tue, Apr 22, 2014 at 10:54:37PM +0300, Ilpo Järvinen wrote:
> On Tue, 22 Apr 2014, Richard Z. wrote:
> 
> > > Layer tag is a *hint* to the renderer, nothing more.
> > 
> > the wiki page says 
> > <<
> > The layer=* tag is one of several methods used to describe vertical 
> > relationships between crossing or overlapping features.
> > >>
> > 
> > Not a single word of a "hint to the renderer" anywhere in the article.
> 
> What would be the other "methods"?

>From wiki key:layer again:
<<
Several other tags can establish or modify vertical relationships explicitly or 
by builtin assumptions. Some of those are level=*, location=*, covered=*, 
highway=steps, 
aerialway=*, power=line, waterway=dam
>>


 
> > Now what is that key:layer anyway? Given that nobody knows or cares how it 
> > works does it do more good than harm? Do we need it at all?
> > Or should we make a fresh start with something well defined and deprecate
> > this mess?
> 
> I personally think that only thing that would need to be added/defined, is 
> sensible defaults for bridges/tunnels (less weight than layer=*) and get 
> "validators" updated. For some yet to be explained reasons, some people 
> spread FUD about that being impossible but it's clearly incorrect claim
> if the implicit default is correctly defined.

that might actually work, but what is the advantage over a JOSM preset
with a layer=1 as default?

> The (supposed) problem with layer=-1 on rivers this thread is about would 
> be magically solved and all those could be eventually be removed (not in a 
> mass-removal but more carefully).

the problem has more causes. But mainly people got used to use the layer=-1 as
a cheap trick to hide all kinds of pesky keepright/JOSM warnings about missing 
bridges, incorrect crossings, waterway crossing waterway and a few more.

The problem is very rarely bridges with missing/incorrect layer but most of the
time the bridges are missing altogether.
The problem would go away if people would add those bridges but this is not 
possible 
unless you know for sure that those are actually bridges - and of course it is 
easier to add layer=-1 to a single river than adding several hundreds of 
bridges.
The problem would also go away if validators would detect this abuse.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Tue, 22 Apr 2014, Richard Z. wrote:

> > Layer tag is a *hint* to the renderer, nothing more.
> 
> the wiki page says 
> <<
> The layer=* tag is one of several methods used to describe vertical 
> relationships between crossing or overlapping features.
> >>
> 
> Not a single word of a "hint to the renderer" anywhere in the article.

What would be the other "methods"?

> Now what is that key:layer anyway? Given that nobody knows or cares how it 
> works does it do more good than harm? Do we need it at all?
> Or should we make a fresh start with something well defined and deprecate
> this mess?

I personally think that only thing that would need to be added/defined, is 
sensible defaults for bridges/tunnels (less weight than layer=*) and get 
"validators" updated. For some yet to be explained reasons, some people 
spread FUD about that being impossible but it's clearly incorrect claim
if the implicit default is correctly defined.

The (supposed) problem with layer=-1 on rivers this thread is about would 
be magically solved and all those could be eventually be removed (not in a 
mass-removal but more carefully).



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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Tue, Apr 22, 2014 at 10:58:35AM +0200, André Pirard wrote:
> On 2014-04-21 22:20, Martin Koppenhoefer wrote :
> >
> > 2014-04-21 20:48 GMT+02:00 Richard Z.  > >:
> >
> > > Without any additional tags like "tunnel=*" or "covered=*", a
> > > "layer=-1" river shouldn't be rendered differently than a
> > "layer=1" or
> > > even in the absence of any "layer" tag. This is a bug in OsmAnd. You
> >
> > except for the the very frequent case when the river with a layer=-1
> > goes through a landuse=* area with a layer=0.
> >
> >
> >
> > +1, as soon as there is any other object on a different layer, be it
> > landuse, a place area or something else, with the lower layer tag you
> > are excluding the river from this feature and putting it below.
> -2
> 
> First because generally a landuse (think of residential) is not a
> physical object but a boundary.  Just like highlighting a municipality
> area by coloring it does not hide what is inside it, coloring a landuse
> must not either.

take "natural" instead of "landuse". How many more exceptions do you
want to make? Is a natural=stone not physical enough for you?

What good are those exceptions anyway?

There is no reason and no justification to tag anything wiht "layer" unless 
it is a bridge, tunnel or similar. So why complicate things?

> The Osmand's (or its renderer's) bug looks much like this.
> To say it more precisely than "it looks bad", It uses dotted lines for
> -1, -2 and probably below. There is no reason why.
> It should be corrected and not be worked around by changing all levels
> all over OSM (and discovering that doing so raises another bug in Osmxor).

Correcting bugs like this in OSM data will raise many hundreds of warnings 
because someone deliberately tagged the river with layer=-1 to obscure all 
those warnings in the first place.

In 99% of cases that I have seen every river randomly tagged with layer=-1
obscures some other 10-100 errors which become visible as soon as you remove 
the improper layer=-1 tag.

Those bugs will remain lurking forever if nobody cares about applying correct
layer tags. The validators do not appear to be capable doing any kind of 
checking
as long as layer(A)!=layer(B) 

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Mon, Apr 21, 2014 at 09:53:21PM +0100, Chris Hill wrote:
> On 21/04/14 21:20, Martin Koppenhoefer wrote:
> >
> >2014-04-21 20:48 GMT+02:00 Richard Z.  >>:
> >
> >> Without any additional tags like "tunnel=*" or "covered=*", a
> >> "layer=-1" river shouldn't be rendered differently than a
> >"layer=1" or
> >> even in the absence of any "layer" tag. This is a bug in OsmAnd. You
> >
> >except for the the very frequent case when the river with a layer=-1
> >goes through a landuse=* area with a layer=0.
> >
> >
> >
> >+1, as soon as there is any other object on a different layer, be
> >it landuse, a place area or something else, with the lower layer
> >tag you are excluding the river from this feature and putting it
> >below.
> 
> Layer is a hint to the renderer. The item with the lowest layer
> value is drawn first, then the next highest and so on. In the
> example of where a road crosses a railway on a bridge, the railway
> (often default layer=0) is drawn, then the road (often layer=1) is
> drawn,casing first then inner and any part that crosses the railway
> obscures that part of the railway.

we don't have a bridge here.

> What you are saying is that the river (layer=-1) is drawn then the
> landuse (layer=0) is drawn over it, obscuring the river. This is
> clearly not intended and not what actually happens in Mapnik
> renders, which is much smarter than that.

in other words mapnik is applying artificial intelligence trying to 
work around obvious errors in OSM data.
 
> Layer tag is a *hint* to the renderer, nothing more.

the wiki page says 
<<
The layer=* tag is one of several methods used to describe vertical 
relationships between crossing or overlapping features.
>>

Not a single word of a "hint to the renderer" anywhere in the article.

If the definition of "key:layer" would become "a hint to the renderer" we 
could clearly abolish it. 
We don't tag for the renderer means ***we do not need hints for the renderer***.

Especially not bad ones.

And how much worth is a "hint to the renderer" if the renderer can only work 
by deliberately ignoring the hint?

Now what is that key:layer anyway? Given that nobody knows or cares how it 
works does it do more good than harm? Do we need it at all?
Or should we make a fresh start with something well defined and deprecate
this mess?

Richard



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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Dave F.]

On 21/04/2014 21:20, Martin Koppenhoefer wrote:


2014-04-21 20:48 GMT+02:00 Richard Z. >:


> Without any additional tags like "tunnel=*" or "covered=*", a
> "layer=-1" river shouldn't be rendered differently than a
"layer=1" or
> even in the absence of any "layer" tag. This is a bug in OsmAnd. You

except for the the very frequent case when the river with a layer=-1
goes through a landuse=* area with a layer=0.



+1, as soon as there is any other object on a different layer, be it 
landuse, a place area or something else, with the lower layer tag you 
are excluding the river from this feature and putting it below.




I'm genuinely surprised how a relatively simple tag can cause such 
confusion amongst experienced mappers. The above is an example of 
incorrect tagging & therefore should be fixed. However, on saying that, 
it doesn't mean that it will automatically be rendered as such. As has 
been said many times previously it is just a *guide* for the renderer, 
who, as with Mapnik, will ignore the layer=* tags in that example & let 
common sense prevail.


Dave F.


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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Andrew Errington]

On Tue, 22 Apr 2014 17:58:35 André Pirard wrote:
> The Osmand's (or its renderer's) bug looks much like this.
> To say it more precisely than "it looks bad", It uses dotted lines for
> -1, -2 and probably below. There is no reason why.
> It should be corrected and not be worked around by changing all levels
> all over OSM (and discovering that doing so raises another bug in Osmxor).

I don't understand.  You say that we should "correct the bug in Osmand", and 
changing the layers is "working around the bug".  Even if Osmand is "fixed", 
tagging layer=-1 on a river is wrong.

The thing that must be corrected is the incorrect use of layer tags!  If this 
raises errors in Osmxor, which I have never heard of, by the way, then Osmxor 
should be changed, perhaps to a warning, not an error (or bug, or whatever it 
does).

Best wishes,

Andrew

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Pieren]

On Mon, Apr 21, 2014 at 10:53 PM, Chris Hill  wrote:

> Layer tag is a *hint* to the renderer, nothing more. In the case of a river
> (or road) passing through a landuse area the renderer doesn't need a hint
> and to say the river is somehow below the landuse does not make sense.

+1
Again, without a complementary tag like "tunnel" or "covered", you can
only speculate about the topology. QA tools report errors if two
features are crossing each other without these additional tags
(road/road, road/river, road/railway, etc... but not a river crossing
a landuse).

Pieren

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[André Pirard]

On 2014-04-21 22:20, Martin Koppenhoefer wrote :
>
> 2014-04-21 20:48 GMT+02:00 Richard Z.  >:
>
> > Without any additional tags like "tunnel=*" or "covered=*", a
> > "layer=-1" river shouldn't be rendered differently than a
> "layer=1" or
> > even in the absence of any "layer" tag. This is a bug in OsmAnd. You
>
> except for the the very frequent case when the river with a layer=-1
> goes through a landuse=* area with a layer=0.
>
>
>
> +1, as soon as there is any other object on a different layer, be it
> landuse, a place area or something else, with the lower layer tag you
> are excluding the river from this feature and putting it below.
-2

First because generally a landuse (think of residential) is not a
physical object but a boundary.  Just like highlighting a municipality
area by coloring it does not hide what is inside it, coloring a landuse
must not either.

Second, because, even if physical like the often debated case of a
forest, where there is a road there is no forest, no plants, it is
interrupted, it does not hide anything and there is no question of
levels where something does not exist.  The same applies for river beds,
railway lines and buildings. In the eyes of a renderer, they are
exclusive with a forest and other "something else".

A different case is a railway line in a tunnel, which is effectively
under ground. In that case, the line must be dotted (in hope that the
source of the data used the same idea and you know where it is.  Never
tag source=GPS in a tunnel ;-))
Don't laugh:  
https://taginfo.openstreetmap.org/tags/source=GPS#combinations  and
combine with "tunnel" ;-)

The Osmand's (or its renderer's) bug looks much like this.
To say it more precisely than "it looks bad", It uses dotted lines for
-1, -2 and probably below. There is no reason why.
It should be corrected and not be worked around by changing all levels
all over OSM (and discovering that doing so raises another bug in Osmxor).

Cheers,

André.




 
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Chris Hill]

On 21/04/14 21:20, Martin Koppenhoefer wrote:


2014-04-21 20:48 GMT+02:00 Richard Z. >:


> Without any additional tags like "tunnel=*" or "covered=*", a
> "layer=-1" river shouldn't be rendered differently than a
"layer=1" or
> even in the absence of any "layer" tag. This is a bug in OsmAnd. You

except for the the very frequent case when the river with a layer=-1
goes through a landuse=* area with a layer=0.



+1, as soon as there is any other object on a different layer, be it 
landuse, a place area or something else, with the lower layer tag you 
are excluding the river from this feature and putting it below.


Layer is a hint to the renderer. The item with the lowest layer value is 
drawn first, then the next highest and so on. In the example of where a 
road crosses a railway on a bridge, the railway (often default layer=0) 
is drawn, then the road (often layer=1) is drawn,casing first then inner 
and any part that crosses the railway obscures that part of the railway.


What you are saying is that the river (layer=-1) is drawn then the 
landuse (layer=0) is drawn over it, obscuring the river. This is clearly 
not intended and not what actually happens in Mapnik renders, which is 
much smarter than that.


Layer tag is a *hint* to the renderer, nothing more. In the case of a 
river (or road) passing through a landuse area the renderer doesn't need 
a hint and to say the river is somehow below the landuse does not make 
sense. The landuse is an arbitary, geopolitical invention, which we find 
useful and does not actually exist, therefore it cannot be above or 
below a river, nor is it an object that somehow needs separating from a 
river. Indeed the river can be part of a landuse area, such as an 
industrial wharf in the same way as a road can be part of a residential 
area.


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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

2014-04-21 20:48 GMT+02:00 Richard Z. :

> > Without any additional tags like "tunnel=*" or "covered=*", a
> > "layer=-1" river shouldn't be rendered differently than a "layer=1" or
> > even in the absence of any "layer" tag. This is a bug in OsmAnd. You
>
> except for the the very frequent case when the river with a layer=-1
> goes through a landuse=* area with a layer=0.



+1, as soon as there is any other object on a different layer, be it
landuse, a place area or something else, with the lower layer tag you are
excluding the river from this feature and putting it below.

cheers,
Martin
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Mon, Apr 21, 2014 at 07:06:16PM +0900, Andrew Errington wrote:
 
> Should I add layer=-1 to all the rivers and streams again?

no, see other email.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Mon, Apr 21, 2014 at 11:42:34AM +0200, Pieren wrote:
> On Sat, Apr 19, 2014 at 1:46 AM, Andrew Errington  
> wrote:
> 
> > I am using OSMAND for navigation, so it's important to have clear maps.  Now
> > that I have downloaded the latest data for this area (which includes my
> > updates) I am much happier with the map I see.
> 
> Without any additional tags like "tunnel=*" or "covered=*", a
> "layer=-1" river shouldn't be rendered differently than a "layer=1" or
> even in the absence of any "layer" tag. This is a bug in OsmAnd. You

except for the the very frequent case when the river with a layer=-1
goes through a landuse=* area with a layer=0.
There is no general agreement that the renderer is supposed to override
the layer and render the river on top of the landuse in this case and
last time I looked the renderers were evenly split about how to render 
this. This is clearly undefined behavior and asking for trouble.

> You clearly admit that you tag for the renderer.

Tagging for the renderer is good as long as it is correct tagging. It is
only wrong when it mean "deliberately tagging contrary to best practice" 
for the purpose of achieving a certain effect (not limited to rendering btw).

His changes (as he explained them) were certainly correct and most likely 
an improvement over the previous state.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Andrew Errington]

Mea culpa, except that the layer=* tag is a hint for the renderer.

Should I add layer=-1 to all the rivers and streams again?

If not, why not?

Best wishes,

Andrew

PS I didn't want to mention the lake that was tagged layer=-2, but I
fixed that too.  Having visited it I can confirm it is indeed on top
of the dirt underneath it.

On 21/04/2014, Pieren  wrote:
> On Sat, Apr 19, 2014 at 1:46 AM, Andrew Errington 
> wrote:
>
>> I am using OSMAND for navigation, so it's important to have clear maps.
>> Now
>> that I have downloaded the latest data for this area (which includes my
>> updates) I am much happier with the map I see.
>
> Without any additional tags like "tunnel=*" or "covered=*", a
> "layer=-1" river shouldn't be rendered differently than a "layer=1" or
> even in the absence of any "layer" tag. This is a bug in OsmAnd. You
> clearly admit that you tag for the renderer.
>
> Pieren
>
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Pieren]

On Sat, Apr 19, 2014 at 1:46 AM, Andrew Errington  wrote:

> I am using OSMAND for navigation, so it's important to have clear maps.  Now
> that I have downloaded the latest data for this area (which includes my
> updates) I am much happier with the map I see.

Without any additional tags like "tunnel=*" or "covered=*", a
"layer=-1" river shouldn't be rendered differently than a "layer=1" or
even in the absence of any "layer" tag. This is a bug in OsmAnd. You
clearly admit that you tag for the renderer.

Pieren

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Andrew Errington]

As I said earlier, I fixed a lot of rivers and waterways nearby that were 
incorrectly tagged as layer=-1.  I removed the layer tag (since it is not 
necessary on a river or stream) and checked all the bridges and tunnels in the 
area.  Some bridges and tunnels did not have a layer tag, which is an error, 
so I added them correctly.

The main reason for doing this (other than to correct poor mapping) is because 
OSMAND draws rivers with 'layer=-1' differently to rivers with no layer tag, 
and it looks bad, especially where there *are* sections of river correctly 
tagged with layer=-1, such as in a tunnel, for example.

I am using OSMAND for navigation, so it's important to have clear maps.  Now 
that I have downloaded the latest data for this area (which includes my 
updates) I am much happier with the map I see.

Best wishes,

Andrew

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Sat, Apr 05, 2014 at 10:14:05PM +0200, Frederik Ramm wrote:
> Hi,
> 
> On 05.04.2014 21:17, Richard Z. wrote:
> > If the road (for whichever reason, valid or not) has layer=-1 and the 
> > forest 
> > just the implicit layer==0, the road should still be drawn above the forest.
> 
> I don't think that this idea is universally accepted.

hm.. I have no strong preference either way but I think rivers and roads should
be treated the same way in the same situation which they apparently are not
in Mapnik.

So it would be good to agree which variant is "more desirable" and mark the 
other
as deprecated.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Sat, Apr 05, 2014 at 11:04:13PM +0300, Ilpo Järvinen wrote:
> On Sat, 5 Apr 2014, Richard Z. wrote:
> 
> > On Fri, Apr 04, 2014 at 09:41:56PM +0200, André Pirard wrote:
> > 
> > In addition, "key:layer" *is not* rendering layer/order.
> > 
> > One example, a road is going through a forest, both should have implicit 
> > "key:layer" ==0. 
> > Obviously they still have a defined rendering order, otherwise our roads 
> > would disappear where they go through forests.
> >
> > If the road (for whichever reason, valid or not) has layer=-1 and the 
> > forest 
> > just the implicit layer==0, the road should still be drawn above the forest.
> 
> Currently roads vanish regardless of the drawing order: 
> 
>   http://www.openstreetmap.org/#map=8/61.493/27.658

thanks for pointing out.

In that case I consider it rather bizarre that in the same situation rivers
don't vanish in Mapnik.

Imho it should be fixed either way.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Frederik Ramm]

Hi,

On 05.04.2014 21:17, Richard Z. wrote:
> If the road (for whichever reason, valid or not) has layer=-1 and the forest 
> just the implicit layer==0, the road should still be drawn above the forest.

I don't think that this idea is universally accepted.

Bye
Frederik

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Sat, 5 Apr 2014, Richard Z. wrote:

> On Fri, Apr 04, 2014 at 09:41:56PM +0200, André Pirard wrote:
> 
> In addition, "key:layer" *is not* rendering layer/order.
> 
> One example, a road is going through a forest, both should have implicit 
> "key:layer" ==0. 
> Obviously they still have a defined rendering order, otherwise our roads 
> would disappear where they go through forests.
>
> If the road (for whichever reason, valid or not) has layer=-1 and the forest 
> just the implicit layer==0, the road should still be drawn above the forest.

Currently roads vanish regardless of the drawing order: 

  http://www.openstreetmap.org/#map=8/61.493/27.658

;-)


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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Fri, Apr 04, 2014 at 09:41:56PM +0200, André Pirard wrote:
> Hi,
> 
> Regarding normalized layers.
> If I can believe my eyes, bridges/culverts are under (uninterrupted
> foil) roads
> :
>  
> bridge=road-1.
> Unless a renderer must assume that, which should be stated in the wiki,
> then bridge=road.
> If I can believe my eyes, 90° crossing rivers/roads run under bridges,
> that is river=bridge-1.
> Unless a renderer must assume that, which should be stated in the wiki,
> then river=bridge.
> A friend of mine says that we must start counting at 1 (like year 1) and
> hence that ground=1 (;-)).
> I'd like to know how many of you agree.  While waiting, let's assume
> ground=0.
> 
> Hence, it depends very much on what the wiki states and we should settle
> that before discussing.
> Assuming assumption, we have road=0, bridge=0, river=0.
> If the renderer does not assume anything we have road=0, bridge=-1 and
> river=-2.

we don't have that. Perhaps you are concluding "uninterrupted level road" 
=> same layer all along the road?
There is no rule like this. You can split a completely level way into many 
parts and assign any of these levels a layer from -5 to 5 (you *should* use
layer<>0 only for segments which are bridge/tunnel etc but elevation is not
relevant).

In addition, "key:layer" *is not* rendering layer/order.

One example, a road is going through a forest, both should have implicit 
"key:layer" ==0. 
Obviously they still have a defined rendering order, otherwise our roads 
would disappear where they go through forests.

If the road (for whichever reason, valid or not) has layer=-1 and the forest 
just the implicit layer==0, the road should still be drawn above the forest.


Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Wed, 2 Apr 2014, Richard Z. wrote:

> On Wed, Apr 02, 2014 at 03:53:25PM +0300, Ilpo Järvinen wrote:
> > On Wed, 2 Apr 2014, Dave Swarthout wrote:
> > 
> > > C'mon guys. Tagging an entire river at layer=-1 is simply not the way to 
> > > do
> > > things, unless it is a covered river or one that runs underground. What
> > > other possible justification is there other than not wanting to do the 
> > > work
> > > of tagging bridges with a layer=1? If you argue it's okay if there aren't
> > > any crossing/overlapping objects do you mean on the entire planet?
> > 
> > C'mon guys. It should be done with sensible defaults rather than forcing 
> > mappers to tell such plain obvious things. Rivers tend to pretty 
> > universally go below bridges, don't you agree?
> 
> yes. It should be done with sensible presets, we can not change the defaults
> for features that are already in use for ages.

This is just misinformation. The default is possible to add even though 
many keep repeating it's impossible. We just need to ensure that the 
layer=* overrides and weights more than the default. Together it would 
ensure that _only_ those cases which do not have layers defined yet get 
affected.

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Tue, Apr 01, 2014 at 11:21:51PM -0700, Bryce Nesbitt wrote:

> April 1st aside: the number of important implicit assumptions is relatively
> small.  Rivers under, power lines over, closed ways under except if they're
> tagged building, etc.  Currently this type of layering is implicit in
> various bits rendering software, but
> it could be formalized at the tag definition level to help meet certain
> mapper expectations.

there are some more assumptions, rivers are visible and not under forests, 
residential
areas maybe others.
The way mapnik handles this is black magic.

Also, when formalizing this we should make a distinction between rendering
order and vertical object relations.

> In the case of the river/highway layer warning: if the warning had never
> existed, chances are the various workaround schemes would never have come
> up.  Rivers would run under roadways, and tagging would be needed only in
> the rare case of a ford or an arroyo with no culvert.

That warning is indeed the cause of lots of hassle. It is not wrong but
until it is balanced by more complete validation of layers, rivers etc
it seems to cause more damage than good.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Wed, Apr 02, 2014 at 03:53:25PM +0300, Ilpo Järvinen wrote:
> On Wed, 2 Apr 2014, Dave Swarthout wrote:
> 
> > C'mon guys. Tagging an entire river at layer=-1 is simply not the way to do
> > things, unless it is a covered river or one that runs underground. What
> > other possible justification is there other than not wanting to do the work
> > of tagging bridges with a layer=1? If you argue it's okay if there aren't
> > any crossing/overlapping objects do you mean on the entire planet?
> 
> C'mon guys. It should be done with sensible defaults rather than forcing 
> mappers to tell such plain obvious things. Rivers tend to pretty 
> universally go below bridges, don't you agree?

yes. It should be done with sensible presets, we can not change the defaults
for features that are already in use for ages.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Pieren]

On Wed, Apr 2, 2014 at 3:10 PM, Ilpo Järvinen  wrote:

> > Rivers tend to pretty universally go below bridges, don't you agree?
>
> Or bridges go above rivers? :-)

^^
Sounds like the glass being half empty or half full. We will never
reconcile the two points of view ;-)

Pieren

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

2014-04-02 15:10 GMT+02:00 Ilpo Järvinen :

> Definately, both :), which was my point. Adding layer in this case is just
> to satisfy some lawyer rather than useful "work".
>




not adding layer tags to objects crossing on different layers is incomplete
data. It can still be rendered "correctly" in most cases, i.e. the "simple"
ones, but this doesn't make the data complete. I agree it is often more a
formal requirement then a practical necessity to tag the bridge with
layer=1 (can be guessed correctly according to common sense for 99.9% of
the cases, agreed), while tagging the river for longer parts with layer=-1
will most probably lead to inconsistencies sooner or later, so I see it as
bad style (though not necessarily "wrong").


cheers,
Martin
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Wed, 2 Apr 2014, Nelson A. de Oliveira wrote:

> On Wed, Apr 2, 2014 at 9:53 AM, Ilpo Järvinen  
> wrote:
> > C'mon guys. It should be done with sensible defaults rather than forcing
> > mappers to tell such plain obvious things. Rivers tend to pretty
> > universally go below bridges, don't you agree?
> 
> Or bridges go above rivers? :-)

Definately, both :), which was my point. Adding layer in this case is just 
to satisfy some lawyer rather than useful "work".

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Nelson A. de Oliveira]

On Wed, Apr 2, 2014 at 9:53 AM, Ilpo Järvinen  wrote:
> C'mon guys. It should be done with sensible defaults rather than forcing
> mappers to tell such plain obvious things. Rivers tend to pretty
> universally go below bridges, don't you agree?

Or bridges go above rivers? :-)

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Wed, 2 Apr 2014, Dave Swarthout wrote:

> C'mon guys. Tagging an entire river at layer=-1 is simply not the way to do
> things, unless it is a covered river or one that runs underground. What
> other possible justification is there other than not wanting to do the work
> of tagging bridges with a layer=1? If you argue it's okay if there aren't
> any crossing/overlapping objects do you mean on the entire planet?

C'mon guys. It should be done with sensible defaults rather than forcing 
mappers to tell such plain obvious things. Rivers tend to pretty 
universally go below bridges, don't you agree?

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Wed, 2 Apr 2014, Martin Koppenhoefer wrote:

> 2014-04-02 13:51 GMT+02:00 Richard Z. :
>   It is not wrong by itself but there are many circumstances
>   where it
>   is plain wrong
> 
> +1, it is not wrong as long as there aren't any crossing / overlapping
> objects that have a different layer in OSM (e.g. no layer tag in OSM =
> implicit layer=0) but are physically or conceptually on the same layer in
> reality. Basically you'd have to put all these other objects as well to
> layer=-1, which in turn would most probably require you to put even more
> objects on layer=-1 and so on.

So how would bridge+layer=1 => bridge+layer=2 transition happen, given 
such a non-sense rule. Definately a road continuing is supposedly "on the 
same layer" as the previous part? Does it imply layer is cast to stone for 
the whole road network because all connections to a node are definately 
sharing the level at the node. Or what did you mean?!?


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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Dave Swarthout]

C'mon guys. Tagging an entire river at layer=-1 is simply not the way to do
things, unless it is a covered river or one that runs underground. What
other possible justification is there other than not wanting to do the work
of tagging bridges with a layer=1? If you argue it's okay if there aren't
any crossing/overlapping objects do you mean on the entire planet?


On Wed, Apr 2, 2014 at 7:07 PM, Martin Koppenhoefer
wrote:

>
> 2014-04-02 13:51 GMT+02:00 Richard Z. :
>
> It is not wrong by itself but there are many circumstances where it
>> is plain wrong
>>
>
>
>
> +1, it is not wrong as long as there aren't any crossing / overlapping
> objects that have a different layer in OSM (e.g. no layer tag in OSM =
> implicit layer=0) but are physically or conceptually on the same layer in
> reality. Basically you'd have to put all these other objects as well to
> layer=-1, which in turn would most probably require you to put even more
> objects on layer=-1 and so on.
>
> cheers,
> Martin
>
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

2014-04-02 13:51 GMT+02:00 Richard Z. :

> It is not wrong by itself but there are many circumstances where it
> is plain wrong
>



+1, it is not wrong as long as there aren't any crossing / overlapping
objects that have a different layer in OSM (e.g. no layer tag in OSM =
implicit layer=0) but are physically or conceptually on the same layer in
reality. Basically you'd have to put all these other objects as well to
layer=-1, which in turn would most probably require you to put even more
objects on layer=-1 and so on.

cheers,
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Wed, Apr 02, 2014 at 10:15:39AM +0200, Pieren wrote:
> On Wed, Apr 2, 2014 at 8:32 AM, Andrew Errington  wrote:
> > I have discovered a bunch of rivers and streams with layer=-1 in my
> > local area.  In my opinion this is simply wrong,
> 
> It's not wrong. It's just another way to use the tag layer. I't not
> because other contributors don't share you opinion that they are
> wrong.

It is not wrong by itself but there are many circumstances where it
is plain wrong. As it happens in many cases where you find long rivers
and streams with layer=-1 one or more of the conditions making it
wrong are met.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Pieren]

On Wed, Apr 2, 2014 at 8:32 AM, Andrew Errington  wrote:
> I have discovered a bunch of rivers and streams with layer=-1 in my
> local area.  In my opinion this is simply wrong,

It's not wrong. It's just another way to use the tag layer. I't not
because other contributors don't share you opinion that they are
wrong.

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Dave Swarthout]

@Andy
"I have discovered a bunch of rivers and streams with layer=-1 in my
local area.  In my opinion this is simply wrong, so I am removing the
layer tag from the river and checking for objects which cross the
river (to tag them with layer=1."

I have done this a bit myself. I came across a river that was tagged with
layer=-3 the other day. I think the layer=1 tag for bridges is understood
to be a default by many mappers but I always include it.


On Wed, Apr 2, 2014 at 1:32 PM, Andrew Errington wrote:

> I have discovered a bunch of rivers and streams with layer=-1 in my
> local area.  In my opinion this is simply wrong, so I am removing the
> layer tag from the river and checking for objects which cross the
> river (to tag them with layer=1.
>
> Best wishes,
>
> Andrew
>
> On 02/04/2014, Bryce Nesbitt  wrote:
> > The present situation is that rivers implicitly render below highways in
> > all common renderings.  That's not necessarily bad. With some formality
> to
> > the layering arrangement, it sure would save a lot of tagging hassle and
> > maintenance.
> >
> > The new cloud tag for example, is clearly to be rendered after everything
> > but the celestial tags.
> >
> > Ahem.
> > April 1st aside: the number of important implicit assumptions is
> relatively
> > small.  Rivers under, power lines over, closed ways under except if
> they're
> > tagged building, etc.  Currently this type of layering is implicit in
> > various bits rendering software, but
> > it could be formalized at the tag definition level to help meet certain
> > mapper expectations.
> >
> > ---
> > In the case of the river/highway layer warning: if the warning had never
> > existed, chances are the various workaround schemes would never have come
> > up.  Rivers would run under roadways, and tagging would be needed only in
> > the rare case of a ford or an arroyo with no culvert.
> >
>
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Andrew Errington]

I have discovered a bunch of rivers and streams with layer=-1 in my
local area.  In my opinion this is simply wrong, so I am removing the
layer tag from the river and checking for objects which cross the
river (to tag them with layer=1.

Best wishes,

Andrew

On 02/04/2014, Bryce Nesbitt  wrote:
> The present situation is that rivers implicitly render below highways in
> all common renderings.  That's not necessarily bad. With some formality to
> the layering arrangement, it sure would save a lot of tagging hassle and
> maintenance.
>
> The new cloud tag for example, is clearly to be rendered after everything
> but the celestial tags.
>
> Ahem.
> April 1st aside: the number of important implicit assumptions is relatively
> small.  Rivers under, power lines over, closed ways under except if they're
> tagged building, etc.  Currently this type of layering is implicit in
> various bits rendering software, but
> it could be formalized at the tag definition level to help meet certain
> mapper expectations.
>
> ---
> In the case of the river/highway layer warning: if the warning had never
> existed, chances are the various workaround schemes would never have come
> up.  Rivers would run under roadways, and tagging would be needed only in
> the rare case of a ford or an arroyo with no culvert.
>

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Bryce Nesbitt]

The present situation is that rivers implicitly render below highways in
all common renderings.  That's not necessarily bad. With some formality to
the layering arrangement, it sure would save a lot of tagging hassle and
maintenance.

The new cloud tag for example, is clearly to be rendered after everything
but the celestial tags.

Ahem.
April 1st aside: the number of important implicit assumptions is relatively
small.  Rivers under, power lines over, closed ways under except if they're
tagged building, etc.  Currently this type of layering is implicit in
various bits rendering software, but
it could be formalized at the tag definition level to help meet certain
mapper expectations.

---
In the case of the river/highway layer warning: if the warning had never
existed, chances are the various workaround schemes would never have come
up.  Rivers would run under roadways, and tagging would be needed only in
the rare case of a ford or an arroyo with no culvert.
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Mon, Mar 24, 2014 at 10:38:08PM +0100, fly wrote:
> On 24.03.2014 20:45, Richard Z. wrote:
> > On Mon, Mar 24, 2014 at 11:02:35AM -0300, Fernando Trebien wrote:
> >> On Mon, Mar 24, 2014 at 10:27 AM, Friedrich Volkmann  wrote:
> 
> As it might be even hard to define the ground level (we just have a
> discussion on talk-de@ about houses built on slops), I would never say
> that an negative layer value is an indicator/synonym for underground.
> 
> >> Again, no mention in the wiki
> >> (http://wiki.openstreetmap.org/wiki/Key:layer) to negative layer
> >> values being used to represent the idea of underground.
> > 
> > not an explicit mention, but if there is an object X1 with implicit layer=0,
> > with no level or location tags, and another object X2 with a layer=-1 than
> > there are not too many possibilities where to find X2. It could be 
> > underground
> > or it could be under a large overhanging rock. Both should have explicit
> > tags to clarify the situation.
> > 
> > 
> >>> No, except for underground rivers. They do exist in karst regions...
> > 
> > we need a way to tag underground rivers and lakes. layer=-1 itself is not
> > sufficient, we need additional tags. Perhaps tunnel=cave but this would
> > only describe part of those phenomena.
> 
> How about location=underground ?

seems good to me.

> covered=yes is another useful tag (eg your overhanging rock)

"covered" is already complicated enough and this might be too much of
stretching the original idea.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Dave Swarthout]

+1 for

Not when you could have other entities passing under the bridges.
I see it as lazy & less accurate. Making OSM more accurate is a primary
consideration when editing


On Tue, Mar 25, 2014 at 7:16 PM, Dave F.  wrote:

> On 14/03/2014 15:57, Pieren wrote:
>
>>
>> You don't see the point where adding one "layer=-1"  is easier than
>> adding 10 "layer=1" ?
>>
>
> Not when you could have other entities passing under the bridges.
> I see it as lazy & less accurate. Making OSM more accurate is a primary
> consideration when editing
>
>  I see the layer tag in "tunnel/bridge" in simple
>> cases but you should not follow all recommendations as fixed in stone.
>>
>
> True, but you should follow the correct ones.
>
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Dave F.]

On 14/03/2014 15:57, Pieren wrote:


You don't see the point where adding one "layer=-1"  is easier than
adding 10 "layer=1" ?


Not when you could have other entities passing under the bridges.
I see it as lazy & less accurate. Making OSM more accurate is a primary 
consideration when editing



I see the layer tag in "tunnel/bridge" in simple
cases but you should not follow all recommendations as fixed in stone.


True, but you should follow the correct ones.

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[fly]

On 24.03.2014 20:45, Richard Z. wrote:
> On Mon, Mar 24, 2014 at 11:02:35AM -0300, Fernando Trebien wrote:
>> On Mon, Mar 24, 2014 at 10:27 AM, Friedrich Volkmann  wrote:

As it might be even hard to define the ground level (we just have a
discussion on talk-de@ about houses built on slops), I would never say
that an negative layer value is an indicator/synonym for underground.

>> Again, no mention in the wiki
>> (http://wiki.openstreetmap.org/wiki/Key:layer) to negative layer
>> values being used to represent the idea of underground.
> 
> not an explicit mention, but if there is an object X1 with implicit layer=0,
> with no level or location tags, and another object X2 with a layer=-1 than
> there are not too many possibilities where to find X2. It could be underground
> or it could be under a large overhanging rock. Both should have explicit
> tags to clarify the situation.
> 
> 
>>> No, except for underground rivers. They do exist in karst regions...
> 
> we need a way to tag underground rivers and lakes. layer=-1 itself is not
> sufficient, we need additional tags. Perhaps tunnel=cave but this would
> only describe part of those phenomena.

How about location=underground ?
covered=yes is another useful tag (eg your overhanging rock)

fly

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Mon, Mar 24, 2014 at 11:02:35AM -0300, Fernando Trebien wrote:
> On Mon, Mar 24, 2014 at 10:27 AM, Friedrich Volkmann  wrote:
> > On 14.03.2014 15:51, Fernando Trebien wrote:
> >> This is a small issue that came up recently in Brazil. In my
> >> understanding, the layer tag has no specific meaning other than to
> >> specify a rendering order.
> >
> > That is a common misconception by people who worked with graphics editing
> > software such as Photoshop and Corel Draw. In these applications, layers are
> > only used for ordering and grouping of objects. As opposed to that abstract
> > layer model, we use a pysical layer model in OSM where layer=0 means
> > ground-level, layer<0 means underground, and layer>0 means above 
> > ground-level.
> 
> This is not written anywhere in the wiki:
> http://wiki.openstreetmap.org/wiki/Key:layer

to clear up this misunderstnding, this has been a relatively recent change 
by me. If you look at it the wording has changed but the practical application
has not.

Earlier there was a longstanding mention of layer=0 as ground-level
along with a complicated definition of what "ground-level" is supposed to be.

I have changed that mainly because the way "ground-level" was defined was
prone to interpretation problems and difficult to define better. 

The new formulation of the kind "higher value" means "higher above" does 
not need the explicit definition of ground-level.
Also the definition of layer=0 as ground-level confused too many people to 
tag elevated roads and similar with layer=1.

However, the new formulation is so that in practice layer=0 will always be 
"ground-level" except perhaps in very complicated urban areas:

<<
Ways passing above other ways on a bridge will have a higher layer value, ways 
passing in tunnels bellow other ways will have lower (negative) values. All 
ways without an explicit value are assumed to have layer 0.
>>

 
> Again, no mention in the wiki
> (http://wiki.openstreetmap.org/wiki/Key:layer) to negative layer
> values being used to represent the idea of underground.

not an explicit mention, but if there is an object X1 with implicit layer=0,
with no level or location tags, and another object X2 with a layer=-1 than
there are not too many possibilities where to find X2. It could be underground
or it could be under a large overhanging rock. Both should have explicit
tags to clarify the situation.


> > No, except for underground rivers. They do exist in karst regions...

we need a way to tag underground rivers and lakes. layer=-1 itself is not
sufficient, we need additional tags. Perhaps tunnel=cave but this would
only describe part of those phenomena.

I am compiling a list of landforms and natural objects that would be worthwile
to map.

Richard


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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Fernando Trebien]

On Mon, Mar 24, 2014 at 10:27 AM, Friedrich Volkmann  wrote:
> On 14.03.2014 15:51, Fernando Trebien wrote:
>> This is a small issue that came up recently in Brazil. In my
>> understanding, the layer tag has no specific meaning other than to
>> specify a rendering order.
>
> That is a common misconception by people who worked with graphics editing
> software such as Photoshop and Corel Draw. In these applications, layers are
> only used for ordering and grouping of objects. As opposed to that abstract
> layer model, we use a pysical layer model in OSM where layer=0 means
> ground-level, layer<0 means underground, and layer>0 means above ground-level.

This is not written anywhere in the wiki:
http://wiki.openstreetmap.org/wiki/Key:layer

> Renderers typically use a different rendering style for underground
> features, e.g. dashed  or greyed-out lines, or these features may even be
> omitted. The only way how renderers can determine whether a feature is
> underground is by looking at the layer tag. tunnel=* and bridge=* do not
> necessarily mean that a feature is underground / above ground. There was
> even a negative voting on this (a proposal for implying layer=-1 or 1
> respectively). And the other way round, not all underground objects are
> tunnels or culverts. A tunnel is a way with an entrance on each end. It is
> not a tunnel if it has a dead end. And what about POIs and areas? It would
> be stupid to tag them as tunnels. The tunnel=* and bridge=* tags do help the
> renderers when it comes to the curved bridge and tunnel signatures, but the
> dashing can only depend on the layer tag.

The concept of "underground" seems more closely related to the tags
level and location:
http://wiki.openstreetmap.org/wiki/Key:level
http://wiki.openstreetmap.org/wiki/Key:location

Again, no mention in the wiki
(http://wiki.openstreetmap.org/wiki/Key:layer) to negative layer
values being used to represent the idea of underground.

>> The wiki, however, states that it is wrong
>> to tag a whole river with layer=-1. The reason for that, as far as I
>> could figure, is because current validators (such as JOSM's or
>> KeepRight's) will not issue a warning on a waterway x highway crossing
>> when their layers are different, leading some users into tagging the
>> river with layer=-1 in order to get rid of warnings about missing
>> bridges and tunnels.
>
> The warning is ok, but the big problem with validators is that mappers mess
> around with the data without local knowledge, just to shut up the validator.
> They connect ways which are not really connected, they insert bridges and
> culverts that do not really exist, and so on. Among these so-called "fixes",
> the layer=-1 on waterways are relatively harmless, because it is so obvious
> that they are wrong. A culvert that has been made up by a sofa mapper is
> much more difficult to correct, because you only know when you go there.

I understand this issue, but don't you think validators could be a
little bit more clever, so that users couldn't trick them? In some
previous message I described some very simple logic that would make
these tricks (in this situation) impossible to work around, and this
would discourage people from using layer=-1 on the rivers.

>> Do you agree that the river can be tagged with layer=-1 as long as
>> this value is correct in relation to the layer of other
>> nearby/crossing ways?
>
> No, except for underground rivers. They do exist in karst regions...
> --
> Friedrich K. Volkmann   http://www.volki.at/
> Adr.: Davidgasse 76-80/14/10, 1100 Wien, Austria
>
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"The speed of computer chips doubles every 18 months." (Moore's law)
"The speed of software halves every 18 months." (Gates' law)

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

> Am 24/mar/2014 um 14:27 schrieb Friedrich Volkmann :
> 
> As opposed to that abstract
> layer model, we use a pysical layer model in OSM where layer=0 means
> ground-level, layer<0 means underground, and layer>0 means above ground-level.


AFAIK it is not defined like this, rather it is meant to describe real world 
stacking (as opposed to rendering order) at a local point: when 2 objects cross 
the one with the higher layer is above, if both layers are equal they are on 
the same level

cheers 
Martin 
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Friedrich Volkmann]

On 14.03.2014 15:51, Fernando Trebien wrote:
> This is a small issue that came up recently in Brazil. In my
> understanding, the layer tag has no specific meaning other than to
> specify a rendering order.

That is a common misconception by people who worked with graphics editing
software such as Photoshop and Corel Draw. In these applications, layers are
only used for ordering and grouping of objects. As opposed to that abstract
layer model, we use a pysical layer model in OSM where layer=0 means
ground-level, layer<0 means underground, and layer>0 means above ground-level.

Renderers typically use a different rendering style for underground
features, e.g. dashed  or greyed-out lines, or these features may even be
omitted. The only way how renderers can determine whether a feature is
underground is by looking at the layer tag. tunnel=* and bridge=* do not
necessarily mean that a feature is underground / above ground. There was
even a negative voting on this (a proposal for implying layer=-1 or 1
respectively). And the other way round, not all underground objects are
tunnels or culverts. A tunnel is a way with an entrance on each end. It is
not a tunnel if it has a dead end. And what about POIs and areas? It would
be stupid to tag them as tunnels. The tunnel=* and bridge=* tags do help the
renderers when it comes to the curved bridge and tunnel signatures, but the
dashing can only depend on the layer tag.

> The wiki, however, states that it is wrong
> to tag a whole river with layer=-1. The reason for that, as far as I
> could figure, is because current validators (such as JOSM's or
> KeepRight's) will not issue a warning on a waterway x highway crossing
> when their layers are different, leading some users into tagging the
> river with layer=-1 in order to get rid of warnings about missing
> bridges and tunnels.

The warning is ok, but the big problem with validators is that mappers mess
around with the data without local knowledge, just to shut up the validator.
They connect ways which are not really connected, they insert bridges and
culverts that do not really exist, and so on. Among these so-called "fixes",
the layer=-1 on waterways are relatively harmless, because it is so obvious
that they are wrong. A culvert that has been made up by a sofa mapper is
much more difficult to correct, because you only know when you go there.

> Do you agree that the river can be tagged with layer=-1 as long as
> this value is correct in relation to the layer of other
> nearby/crossing ways?

No, except for underground rivers. They do exist in karst regions...

-- 
Friedrich K. Volkmann   http://www.volki.at/
Adr.: Davidgasse 76-80/14/10, 1100 Wien, Austria

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

> Am 16/mar/2014 um 01:42 schrieb "Richard Z." :
> 
> Also building=bridge is the wrong tag for this bridge



why? Let's be cautious with judgements like "wrong tag" and even more in 
situations where there is not clearly a generally adopted tagging scheme (like 
for bridges).

cheers,
Martin
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Sat, Mar 15, 2014 at 03:19:36PM -0300, Fernando Trebien wrote:

> Situation 1 happens in many other cities across the world, and if you
> tag the bridge as layer=1, you may end up inverting the rendering
> order of highways, leading to this:
> http://www.openstreetmap.org/way/138032009

what exactly is the problem here? Colour artefacts on the Quai des Gevres?
If it is affected by the layer than it is a bug in Mapnik - and no, we 
should not use layer to fix bugs in Mapnik.

Looking at the data in JOSM I see a few problems - for example there 
is no reason why this particular way should have any layer tag at all.
It seems completely useless and one of the reasons I want to enforce
the "no layer tag without a bridge/tunnel" rule which would catch
similar accidents.

While not wrong in this case it is also not needed to have the bridge 
at layer=2.

Also building=bridge is the wrong tag for this bridge (tagging for 
Mapnik again ?) but if it is used at all the ways entering the bridge 
ought at least share a node with the bridge where they are entering it.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Mann]

On Sat, Mar 15, 2014 at 7:31 PM, Peter Wendorff
wrote:

> > Situation 1 happens in many other cities across the world, and if you
> > tag the bridge as layer=1, you may end up inverting the rendering
> > order of highways, leading to this:
> > http://www.openstreetmap.org/way/138032009
> good point, but I would consider this a bug independent of rendering as
> the same may occur on the way below the bridge as well, if there's a
> join of that way with another one without a layer tag.x
>
> anyone going to report this as a bug in the stylesheet?
>
> regards
> Peter
>
>
It's exactly this reason why the roads should be at a single layer (except
the underpass) in a given vicinity, and the river set to one layer lower.
If you want to make all the roads layer=1, then feel free, but it's easier
to make the river layer=-1.

It's not a bug. The data is wrong. No renderer could reasonably be asked to
make sense of that mess.
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Peter Wendorff]

Am 15.03.2014 19:19, schrieb Fernando Trebien:
> Here are a few arguable reasons to split the waterway and tag it with 
> layer=-1:
> 1. Bridges may come in pairs for dual carriageways. In this case, it's
> a single layer tag for the waterway versus 2 layer tags for the
> bridges. This may happen many times in a row. In this case, it makes
> sense to split the waterway at 1 point (dividing into "urban" and "not
> urban" parts) and tag the whole urban part with layer=-1. That's the
> case in my hometown (54 tags, one for every bridge vs 1 tag only + 1
> split waterway), see here towards the East:
> http://www.openstreetmap.org/#map=17/-30.04781/-51.22689
On the other hand you don't have to split anything if you put the layer
tag on the bridges because the bridge is already a separate object.

And even bridges span several parallel osm-ways often: cyclepaths
footpaths, streets, railway lines... along the waterway, one sided or
both-sided.

> 2. If you split only near the bridges, the name of the waterway will
> be rendered between the bridges, which is the optimal position. (But
> this "could" be considered mapping for the renderer.)
This is heavily mapping for the renderer. A good and powerful renderer would
a) join ways with the same name but different "detail" tags for layer
positioning
b) place the label where no bridge or way above the tunnel is in
conflict regarding the space on the canvas.

This may not be the case out of performance reasons for an online
rendering system like the mapnik stylesheet on osm.org, but that's
another issue.

> Situation 1 happens in many other cities across the world, and if you
> tag the bridge as layer=1, you may end up inverting the rendering
> order of highways, leading to this:
> http://www.openstreetmap.org/way/138032009
good point, but I would consider this a bug independent of rendering as
the same may occur on the way below the bridge as well, if there's a
join of that way with another one without a layer tag.x

anyone going to report this as a bug in the stylesheet?

regards
Peter


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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Sat, Mar 15, 2014 at 02:06:13PM -0300, Fernando Trebien wrote:
> "the validator will only prevent the most obvious errors but will give
> you no clue how to fix them correctly"
> 
> I know. But two or three rounds of trial and error with the validator
> should be enough to bring a new user to an acceptable representation.

the validator has no idea how the crossing is supposed to look like, this
is a very optimistic assumption optimistic for anything but the simplest 
cases.
 

> "or one of covered,location,indoor,steps,lift or level, maybe more."
> 
> I have to read more about them an check their usage, but they could
> all be incorporated in the same rule in the validator. It's just a few
> extra values in a set referred to in a rule. Surely this set can grow
> over time.

I have a bunch of search strings for JOSM on my user page,
  https://wiki.openstreetmap.org/wiki/User:RicoZ
use those as tests for the assumptions. In most part of the world what 
they match are obvious errors - with the exception of some parts of 
Chicago City which I do not know well enough to judge what is going on
there.

Reply to "level" related things in next email.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Fernando Trebien]

Here are a few arguable reasons to split the waterway and tag it with layer=-1:
1. Bridges may come in pairs for dual carriageways. In this case, it's
a single layer tag for the waterway versus 2 layer tags for the
bridges. This may happen many times in a row. In this case, it makes
sense to split the waterway at 1 point (dividing into "urban" and "not
urban" parts) and tag the whole urban part with layer=-1. That's the
case in my hometown (54 tags, one for every bridge vs 1 tag only + 1
split waterway), see here towards the East:
http://www.openstreetmap.org/#map=17/-30.04781/-51.22689
2. If you split only near the bridges, the name of the waterway will
be rendered between the bridges, which is the optimal position. (But
this "could" be considered mapping for the renderer.)

Situation 1 happens in many other cities across the world, and if you
tag the bridge as layer=1, you may end up inverting the rendering
order of highways, leading to this:
http://www.openstreetmap.org/way/138032009

"(The 'level' confusion again.)"

If this is a common mistake, let's write the distinction at the very
top of the respective article in the wiki.

On Sat, Mar 15, 2014 at 1:39 PM, Frank Little  wrote:
> Fernando Trebien wrote:
>>
>> Alright. I see that "applying layer to long ways" is bad for several
>> reasons. Surely this could be turned into a validation warning.
>>
>> But what's the difference between tagging the bridge with layer=1 and
>> tagging the river underneath with layer=-1? Some people seem to think
>> that both are necessary, many think it's best to use layer=1 on the
>> bridge, I'm saying that layer=-1 on the river (let's say a short
>> section, not the entire length) is "equivalent". Is it not equivalent?
>> Is it wrong? If it is wrong, why is it wrong?
>>
> I don't think 'wrong' is the way to approach this; afaik, they are indeed
> equivalent.
> There are four alternatives which mappers follow, none of which are 'wrong':
> tag the bridge segment, tag the water segment under the bridge, tag both,
> tag neither.
>
> I've run waterway=stream or =canal (or =ditch, I think) through a few of the
> small rivers and streams here in the Netherlands. Roads need splitting to
> make bridges, so it makes sense to do all the relevant tagging on the road
> segment with the bridge tag when you are working on it.
>
> I don't have any reason to split the waterway=*, so I just draw on without
> stopping. Since I put the name on the waterway and not on the riverbank, it
> leaves it to the renderer to find a good place to fit in the
> river/stream/canal name. In principle, that should mean a cleaner map if the
> renderer can work out the proper placement (difficult job, though).
>
> So I would be against splitting the waterway at a bridge and tagging it
> layer=-1 on practical grounds. And you can be sure that it would cause
> confusion with other mappers who would imagine that you are trying to model
> an inverted siphon with the piece of waterway tagged layer=-1, or that you
> had simply made a mistake. (The 'level' confusion again.)
>
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Fernando Trebien]

I thought a bit more and this statement I said is incorrect:

"Correct, let's add "within the same level" to all of those rules, and
assume level=0 when level is not specified in a tag. Then they all
work also for indoor mapping."

The correct wording of those warning rules, taking indoor mapping into
account, should be:

---
If level is missing, use the value of location instead for the
following rules. Otherwise, consider it equal to 0.

When layer is equal between both ways, and so is level, warn when:
1. The ways are unconnected (ie. they just overlap without sharing a node).
2. The ways are connected, one way is a waterway and the other is a
highway and the connection is not explicitly a ford or a dam.

When only level is equal between both ways, warn when:
3. The ways have different layer value and both are missing a tunnel
or a bridge tag.
4. The layer value of a bridge is inferior to that of a way that is
not a bridge.
5. The layer value of a tunnel is superior to that of a way that is
not a tunnel.

In addition, also warn when location=underground/underwater and level
> 0, and when location=overground and level < 0.
---

I thought about the meaning of covered and steps, but they don't say
anything about the vertical order of the overlapping elements, so it
may be interesting to get users to declare that order when ways
overlap within the same level.

Please see if you can find a situation that would not be identified by
those rules, or one that would be identified incorrectly.

On Sat, Mar 15, 2014 at 2:06 PM, Fernando Trebien
 wrote:
> "the validator will only prevent the most obvious errors but will give
> you no clue how to fix them correctly"
>
> I know. But two or three rounds of trial and error with the validator
> should be enough to bring a new user to an acceptable representation.
>
> "there is no difference between connections in endpoints or in a
> crossing point as far as I can tell."
>
> You're right. I should have used "overlap" not "cross". That's what I
> meant really. If a waterway and a highway cross, that means they share
> a common node, so it represents a ford and maybe a dam. If they
> overlap but do not cross, they should, in principle, be in different
> vertical positions, so they should have a different value in the
> "layer" tag.
>
> "or one of covered,location,indoor,steps,lift or level, maybe more."
>
> I have to read more about them an check their usage, but they could
> all be incorporated in the same rule in the validator. It's just a few
> extra values in a set referred to in a rule. Surely this set can grow
> over time.
>
> "except for indoor mapping and maybe other weird cases."
>
> I'm not so much involved with indoor mapping yet, but I think the
> rules would still apply. What I know about indoor mapping (possibly
> too little): it is being done in such a way that people will first
> filter by level and then render. So "layer" probably applies within
> "level". If you have two ways that overlap at the same level but do
> share a node, they must sit at different layers, right? They must be
> vertically displaced, so one of them should be an indoor "tunnel" and
> the other should be an indoor "bridge" (or something alike), right?
>
> "also railways?"
>
> As far as I can imagine, it should apply to railways too. Also to
> combinations of railways with highways, and railways with waterways.
> (If it does not, please show me an example.)
>
> "more general: not connected, different layer values and not one of
> bridge,tunnel,covered,location,indoor,steps,lift, no level tag and
> a few more things to take into account."
>
> I believe you mean that these propositions are joined with "AND"
> logic: not connected AND different layer values AND not of
> {bridge,tunnel,...} AND no level tag", right?
>
> Different layer values AND not one of {bridge,tunnel,...} will issue a
> warning for the way without bridge=* or layer=* that goes underneath
> bridge=yes+layer=1, right?
>
> "identical to d?"
>
> Exactly, that's the point I'm trying to state. Layer is a relative
> value, its actual values should not be assigned any special meaning.
> Layer=0 does not mean ground level, and layer=-1 does not mean
> underground nor should be forbidden for rivers (as long as it obeys
> the other thumb rule: "use layer only in short ways or short spans of
> a way").
>
> "unless indoor or other strange cases"
>
> Correct, let's add "within the same level" to all of those rules, and
> assume level=0 when level is not specified in a tag. Then they all
> work also for indoor mapping.
>
> "It is a lot easier saying that every bridge and tunnel must have a
> layer tag and enforce that than catching all the situations mentioned
> in situation "d"."
>
> Yes but it is also much harder to get everyone in the world to follow
> it. Even a person that knows that rule may forget to apply it
> sometimes. I know that this same reason does not apply to many other
> similar situations in which a validation rule 

Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Fernando Trebien]

"the validator will only prevent the most obvious errors but will give
you no clue how to fix them correctly"

I know. But two or three rounds of trial and error with the validator
should be enough to bring a new user to an acceptable representation.

"there is no difference between connections in endpoints or in a
crossing point as far as I can tell."

You're right. I should have used "overlap" not "cross". That's what I
meant really. If a waterway and a highway cross, that means they share
a common node, so it represents a ford and maybe a dam. If they
overlap but do not cross, they should, in principle, be in different
vertical positions, so they should have a different value in the
"layer" tag.

"or one of covered,location,indoor,steps,lift or level, maybe more."

I have to read more about them an check their usage, but they could
all be incorporated in the same rule in the validator. It's just a few
extra values in a set referred to in a rule. Surely this set can grow
over time.

"except for indoor mapping and maybe other weird cases."

I'm not so much involved with indoor mapping yet, but I think the
rules would still apply. What I know about indoor mapping (possibly
too little): it is being done in such a way that people will first
filter by level and then render. So "layer" probably applies within
"level". If you have two ways that overlap at the same level but do
share a node, they must sit at different layers, right? They must be
vertically displaced, so one of them should be an indoor "tunnel" and
the other should be an indoor "bridge" (or something alike), right?

"also railways?"

As far as I can imagine, it should apply to railways too. Also to
combinations of railways with highways, and railways with waterways.
(If it does not, please show me an example.)

"more general: not connected, different layer values and not one of
bridge,tunnel,covered,location,indoor,steps,lift, no level tag and
a few more things to take into account."

I believe you mean that these propositions are joined with "AND"
logic: not connected AND different layer values AND not of
{bridge,tunnel,...} AND no level tag", right?

Different layer values AND not one of {bridge,tunnel,...} will issue a
warning for the way without bridge=* or layer=* that goes underneath
bridge=yes+layer=1, right?

"identical to d?"

Exactly, that's the point I'm trying to state. Layer is a relative
value, its actual values should not be assigned any special meaning.
Layer=0 does not mean ground level, and layer=-1 does not mean
underground nor should be forbidden for rivers (as long as it obeys
the other thumb rule: "use layer only in short ways or short spans of
a way").

"unless indoor or other strange cases"

Correct, let's add "within the same level" to all of those rules, and
assume level=0 when level is not specified in a tag. Then they all
work also for indoor mapping.

"It is a lot easier saying that every bridge and tunnel must have a
layer tag and enforce that than catching all the situations mentioned
in situation "d"."

Yes but it is also much harder to get everyone in the world to follow
it. Even a person that knows that rule may forget to apply it
sometimes. I know that this same reason does not apply to many other
similar situations in which a validation rule would be much more
complex than that.

"With some luck, you can restrict "d" to waterways and it becomes "easy"."

Fair enough, since the current problem mostly concerns waterways. I
just tried to arrive at a more generic rule, which I believed would be
more useful in the long term.

On Fri, Mar 14, 2014 at 5:12 PM, Richard Z.  wrote:
> On Fri, Mar 14, 2014 at 03:55:39PM -0300, Fernando Trebien wrote:
>> I don't think you should be required to check the river's layer tag.
>> Validators should do this job for you, it's quite easy to write a rule
>> for that.
>
> validators can check for many errors but if you want to change
> anything you have to understand the whole situation.
> Imagine you want to add a new bridge to a complex freeway intersection
> with junctions and overpasses.. the validator will only prevent the
> most obvious errors but will give you no clue how to fix them
> correctly.
>
>> Given two ways that cross internally (excluding connections at
>> endpoints), and considering the "layer value" defined explicitly in a
>> tag or implicitly 0 when the tag is missing, have the validator issue
>> a warning in the following situations:
>
> there is no difference between connections in endpoints or in a crossing
> point as far as I can tell.
>
>> 1. The ways have the same layer value and are unconnected. (They
>> should be connected, or else something is surely missing. This could
>> actually be considered an "error".)
>
> except for aerial ways and similar exceptions
>
>> 1.1. Also warn if if one way is a waterway and the other is a highway
>> and the connection is not explicitly a ford. (It should be, for
>> clarity. If it's not, it's also possibly not a ford, ther

Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Frank Little]

Fernando Trebien wrote:

Alright. I see that "applying layer to long ways" is bad for several
reasons. Surely this could be turned into a validation warning.

But what's the difference between tagging the bridge with layer=1 and
tagging the river underneath with layer=-1? Some people seem to think
that both are necessary, many think it's best to use layer=1 on the
bridge, I'm saying that layer=-1 on the river (let's say a short
section, not the entire length) is "equivalent". Is it not equivalent?
Is it wrong? If it is wrong, why is it wrong?

I don't think 'wrong' is the way to approach this; afaik, they are indeed 
equivalent.
There are four alternatives which mappers follow, none of which are 'wrong': 
tag the bridge segment, tag the water segment under the bridge, tag both, tag 
neither.


I've run waterway=stream or =canal (or =ditch, I think) through a few of the 
small rivers and streams here in the Netherlands. Roads need splitting to make 
bridges, so it makes sense to do all the relevant tagging on the road segment 
with the bridge tag when you are working on it.


I don't have any reason to split the waterway=*, so I just draw on without 
stopping. Since I put the name on the waterway and not on the riverbank, it 
leaves it to the renderer to find a good place to fit in the 
river/stream/canal name. In principle, that should mean a cleaner map if the 
renderer can work out the proper placement (difficult job, though).


So I would be against splitting the waterway at a bridge and tagging it 
layer=-1 on practical grounds. And you can be sure that it would cause 
confusion with other mappers who would imagine that you are trying to model an 
inverted siphon with the piece of waterway tagged layer=-1, or that you had 
simply made a mistake. (The 'level' confusion again.) 



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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Fernando Trebien]

Alright. I see that "applying layer to long ways" is bad for several
reasons. Surely this could be turned into a validation warning.

But what's the difference between tagging the bridge with layer=1 and
tagging the river underneath with layer=-1? Some people seem to think
that both are necessary, many think it's best to use layer=1 on the
bridge, I'm saying that layer=-1 on the river (let's say a short
section, not the entire length) is "equivalent". Is it not equivalent?
Is it wrong? If it is wrong, why is it wrong?

On Sat, Mar 15, 2014 at 12:53 PM, Frank Little  wrote:
> Martin Koppenhoefer wrote:
>>>
>>> Am 14/mar/2014 um 15:51 schrieb Fernando Trebien
>>> :
>>>
>>> Do you agree that the river can be tagged with layer=-1 as long as
>>> this value is correct in relation to the layer of other
>>> nearby/crossing ways?
>>
>>
>> I would discourage you to do so. Layer tags should only be applied to ways
>> that actually cross other objects on different layers (ie without
>> intersecting them).
>>
> I agree totally with: "Layer tags should only be applied to ways that
> actually cross other objects."
>
> At its simplest, a layer tag is a hint to a renderer which of  two crossing
> ways should be rendered later (i.e. on top). If a renderer does not apply
> the real world knowledge that a bridge (by its definition) crosses over a
> way (road, water, whatever) underneath, then it can still take the hint to
> render it correctly. The renderers have no problem interpreting the
> situation correctly, with or without the layer tag, afaik.
>
> A layer tag is not a way to define the relative height of different objects.
> Some of the discussion on the proposal's talk page is confused about that.
>
> I would tag the structure (bridge or tunnel) with a layer tag*.
> I would not tag a river or stream along its entire length.
>
> Rivers, streams, canals, etc. are surface features (in most cases). The mere
> fact that the bed of a waterway is often  at a lower level than the
> surrounding ground level is not relevant for the layer tag since hinting for
> correct rendering is not necessary. (In the Netherlands and other polder
> areas, waterways are often above the surrounding area.)
>
> *Actually, as I made clear on talk when we had this discussion very
> recently, I would prefer not to use the layer tag at all in most of these
> cases. The fact that somewhere between one quarter (taginfo) and one third
> (overpass turbo samples in the Netherlands) do not use a layer tag with
> bridges indicates to me that it is not as clear cut as people are
> suggesting. (Note: I realise that there are specific cases where explicit
> tagging for layer hinting is necessary (e.g. bridges or viaducts layered
> vertically). These are relatively rare.)
>
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-- 
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+55 (51) 9962-5409

"The speed of computer chips doubles every 18 months." (Moore's law)
"The speed of software halves every 18 months." (Gates' law)

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Frank Little]

Martin Koppenhoefer wrote:
Am 14/mar/2014 um 15:51 schrieb Fernando Trebien 
:


Do you agree that the river can be tagged with layer=-1 as long as
this value is correct in relation to the layer of other
nearby/crossing ways?


I would discourage you to do so. Layer tags should only be applied to ways 
that actually cross other objects on different layers (ie without 
intersecting them).


I agree totally with: "Layer tags should only be applied to ways that actually 
cross other objects."


At its simplest, a layer tag is a hint to a renderer which of  two crossing 
ways should be rendered later (i.e. on top). If a renderer does not apply the 
real world knowledge that a bridge (by its definition) crosses over a way 
(road, water, whatever) underneath, then it can still take the hint to render 
it correctly. The renderers have no problem interpreting the situation 
correctly, with or without the layer tag, afaik.


A layer tag is not a way to define the relative height of different objects. 
Some of the discussion on the proposal's talk page is confused about that.


I would tag the structure (bridge or tunnel) with a layer tag*.
I would not tag a river or stream along its entire length.

Rivers, streams, canals, etc. are surface features (in most cases). The mere 
fact that the bed of a waterway is often  at a lower level than the 
surrounding ground level is not relevant for the layer tag since hinting for 
correct rendering is not necessary. (In the Netherlands and other polder 
areas, waterways are often above the surrounding area.)


*Actually, as I made clear on talk when we had this discussion very recently, 
I would prefer not to use the layer tag at all in most of these cases. The 
fact that somewhere between one quarter (taginfo) and one third (overpass 
turbo samples in the Netherlands) do not use a layer tag with bridges 
indicates to me that it is not as clear cut as people are suggesting. (Note: I 
realise that there are specific cases where explicit tagging for layer hinting 
is necessary (e.g. bridges or viaducts layered vertically). These are 
relatively rare.) 



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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Peter Wendorff]

Hi John,
yes, that's one possibility; knew that already, but thanks for pointing
the list to the link.

regards
Peter

Am 15.03.2014 14:16, schrieb John Packer:
> I believe there was a proposal for tagging a bridge separately:
> man_made=bridge. I think it would be really nice to have the actual outline
> of the bridge rendered
> Em 15/03/2014 10:02, "Peter Wendorff"  escreveu:
> 
>> Hi,
>>
>> I agree partially with you here.
>> Yes, adding bridges in addition to the road is possible and may be a
>> good idea.
>> What we currently map as being a bridge in fact is the property of "the
>> road is on a bridge" instead.
>> Changing the current tagging scheme to "duplicate the corresponding
>> segment of the way and tag the bridge as a separate, but again linear
>> object" is worse in all but one point.
>> The only point this is better in is that a street with a continuous name
>> may not have to be splitted because of the bridge; but on the other hand
>> we do so for anything else, too: speed restrictions, footway or not,
>> highway type, surface and anything else; so it doesn't solve an issue
>> dedicated to bridges.
>>
>> On the other hand it doesn't solve the issue with multiple parallel ways
>> on the same bridge, e.g. considering a dual carriage way on one bridge
>> construction we currently map the property "road is on a bridge" again
>> on both parts of the dual carriage way independently, but it's
>> impossible to decide from the data (usually) if it's one bridge or two
>> bridges.
>> Your proposal to duplicate the way does not solve this issue either, as
>> you would still need two separate ways here.
>>
>> regards
>> Peter
>>
>>
>> Am 15.03.2014 13:25, schrieb André Pirard:
>>> Hi,
>>>
>>> I wonder why we make bridges split and split and split the roads.
>>> In reality, bridges are pieces of concrete or stonework at level -1
>>> under an uninterrupted foil of tarmac at level 0.
>>> Or at level 0 if it's understood that the renderer knows what's a bridge.
>>> And the renderer knows, as it draws two thin stripes beside the road.
>>> So, a bridge can be a little way segment overlaying the road.
>>> This lets the routing software ignore the unnecessary complication of
>>> having to account for bridges as part of the route.
>>> This lets the bridge having its own attributes, unrelated to the road,
>>> for example a different name.
>>> This makes obsolete discussions wondering if the bridge must be split in
>>> two because the road changes in the middle.
>>> Etc. etc., all pieces clutch in very neatly.
>>> And BTW, this is similar to tunnel=culvert which is an optional feature
>>> of a bridge and that surprises no one at layer -1.
>>> And now, if we put bridges and culverts at -1, the rivers or streams are
>>> normally at -2.
>>> Tunnels (inside which the road runs) should be segments too, at level +1
>>> or 0.
>>>
>>> I have tagged a number of streams and rivers at -2 -1 0 and I find it
>>> appreciable to have an instant view of where the complete main stream
>>> is, if not exaggeratedly long, as well as less prone to errors.
>>>
>>> Cheers,
>>>
>>> André.
>>>
>>>
>>>
>>>
>>>
>>>
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>>
>>
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> 
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Sat, Mar 15, 2014 at 01:25:16PM +0100, André Pirard wrote:
> Hi,
> 
> I wonder why we make bridges split and split and split the roads.

do not like that too much either.

> In reality, bridges are pieces of concrete or stonework at level -1
> under an uninterrupted foil of tarmac at level 0.

but in our model we don't map the concret, nor do we map cellars instead
of houses. We map bridges as a property of the road.

There is also the possibility to use man_made=bridge instead.

> Or at level 0 if it's understood that the renderer knows what's a bridge.
> And the renderer knows, as it draws two thin stripes beside the road.
> So, a bridge can be a little way segment overlaying the road.

it must be somehow connected to the road though. Do you advocate overlapping
ways?


> And BTW, this is similar to tunnel=culvert which is an optional feature
> of a bridge and that surprises no one at layer -1.
> And now, if we put bridges and culverts at -1, the rivers or streams are
> normally at -2.
> Tunnels (inside which the road runs) should be segments too, at level +1
> or 0.
> 
> I have tagged a number of streams and rivers at -2 -1 0 and I find it
> appreciable to have an instant view of where the complete main stream
> is, if not exaggeratedly long, as well as less prone to errors.

I think everyone else who will come across this tagging will remove
your layer tags as incorrect.

Seems to me the wiki should be kept in sync better.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[John Packer]

I believe there was a proposal for tagging a bridge separately:
man_made=bridge. I think it would be really nice to have the actual outline
of the bridge rendered
Em 15/03/2014 10:02, "Peter Wendorff"  escreveu:

> Hi,
>
> I agree partially with you here.
> Yes, adding bridges in addition to the road is possible and may be a
> good idea.
> What we currently map as being a bridge in fact is the property of "the
> road is on a bridge" instead.
> Changing the current tagging scheme to "duplicate the corresponding
> segment of the way and tag the bridge as a separate, but again linear
> object" is worse in all but one point.
> The only point this is better in is that a street with a continuous name
> may not have to be splitted because of the bridge; but on the other hand
> we do so for anything else, too: speed restrictions, footway or not,
> highway type, surface and anything else; so it doesn't solve an issue
> dedicated to bridges.
>
> On the other hand it doesn't solve the issue with multiple parallel ways
> on the same bridge, e.g. considering a dual carriage way on one bridge
> construction we currently map the property "road is on a bridge" again
> on both parts of the dual carriage way independently, but it's
> impossible to decide from the data (usually) if it's one bridge or two
> bridges.
> Your proposal to duplicate the way does not solve this issue either, as
> you would still need two separate ways here.
>
> regards
> Peter
>
>
> Am 15.03.2014 13:25, schrieb André Pirard:
> > Hi,
> >
> > I wonder why we make bridges split and split and split the roads.
> > In reality, bridges are pieces of concrete or stonework at level -1
> > under an uninterrupted foil of tarmac at level 0.
> > Or at level 0 if it's understood that the renderer knows what's a bridge.
> > And the renderer knows, as it draws two thin stripes beside the road.
> > So, a bridge can be a little way segment overlaying the road.
> > This lets the routing software ignore the unnecessary complication of
> > having to account for bridges as part of the route.
> > This lets the bridge having its own attributes, unrelated to the road,
> > for example a different name.
> > This makes obsolete discussions wondering if the bridge must be split in
> > two because the road changes in the middle.
> > Etc. etc., all pieces clutch in very neatly.
> > And BTW, this is similar to tunnel=culvert which is an optional feature
> > of a bridge and that surprises no one at layer -1.
> > And now, if we put bridges and culverts at -1, the rivers or streams are
> > normally at -2.
> > Tunnels (inside which the road runs) should be segments too, at level +1
> > or 0.
> >
> > I have tagged a number of streams and rivers at -2 -1 0 and I find it
> > appreciable to have an instant view of where the complete main stream
> > is, if not exaggeratedly long, as well as less prone to errors.
> >
> > Cheers,
> >
> > André.
> >
> >
> >
> >
> >
> >
> > ___
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> >
>
>
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Peter Wendorff]

Hi,

I agree partially with you here.
Yes, adding bridges in addition to the road is possible and may be a
good idea.
What we currently map as being a bridge in fact is the property of "the
road is on a bridge" instead.
Changing the current tagging scheme to "duplicate the corresponding
segment of the way and tag the bridge as a separate, but again linear
object" is worse in all but one point.
The only point this is better in is that a street with a continuous name
may not have to be splitted because of the bridge; but on the other hand
we do so for anything else, too: speed restrictions, footway or not,
highway type, surface and anything else; so it doesn't solve an issue
dedicated to bridges.

On the other hand it doesn't solve the issue with multiple parallel ways
on the same bridge, e.g. considering a dual carriage way on one bridge
construction we currently map the property "road is on a bridge" again
on both parts of the dual carriage way independently, but it's
impossible to decide from the data (usually) if it's one bridge or two
bridges.
Your proposal to duplicate the way does not solve this issue either, as
you would still need two separate ways here.

regards
Peter


Am 15.03.2014 13:25, schrieb André Pirard:
> Hi,
> 
> I wonder why we make bridges split and split and split the roads.
> In reality, bridges are pieces of concrete or stonework at level -1
> under an uninterrupted foil of tarmac at level 0.
> Or at level 0 if it's understood that the renderer knows what's a bridge.
> And the renderer knows, as it draws two thin stripes beside the road.
> So, a bridge can be a little way segment overlaying the road.
> This lets the routing software ignore the unnecessary complication of
> having to account for bridges as part of the route.
> This lets the bridge having its own attributes, unrelated to the road,
> for example a different name.
> This makes obsolete discussions wondering if the bridge must be split in
> two because the road changes in the middle.
> Etc. etc., all pieces clutch in very neatly.
> And BTW, this is similar to tunnel=culvert which is an optional feature
> of a bridge and that surprises no one at layer -1.
> And now, if we put bridges and culverts at -1, the rivers or streams are
> normally at -2.
> Tunnels (inside which the road runs) should be segments too, at level +1
> or 0.
> 
> I have tagged a number of streams and rivers at -2 -1 0 and I find it
> appreciable to have an instant view of where the complete main stream
> is, if not exaggeratedly long, as well as less prone to errors.
> 
> Cheers,
> 
> André.
> 
> 
> 
> 
> 
> 
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

> Am 14/mar/2014 um 19:55 schrieb Fernando Trebien :
> 
> I don't think you should be required to check the river's layer tag.
> Validators should do this job for you, it's quite easy to write a rule
> for that.


first you'll have to download all data along this river in order to make this 
work,seems easier to download all data along a bridge when you add it then to 
put layer tags on long ways which tend to extend into not downloaded areas when 
you edit

cheers,
Martin
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

> Am 14/mar/2014 um 16:35 schrieb Fernando Trebien :
> 
> From this logic, layer=-1 means the object is >rendered< beneath
> anything that has layer=0 (or, conversely, that anything with layer=0
> is rendered on top of anything with layer=-1). It does not mean that
> it >is< in fact below it (though it almost always is).


no, the opposite is true, you will render stuff as you like (when using dashed 
lines for underground features you might opt to render them above other lines 
for instance), but the real world stacking order is given by the layer tag

cheers,
Martin
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

> Am 14/mar/2014 um 16:36 schrieb Pieren :
> 
> Real case from real world : a deep ditch where the stream is not
> "underground" but below the "ground" level, is crossing a village
> where we have 10 bridges. Either you add 10 times "layer=1" on the
> bridges or you add 1 time "layer=-1" on the stream.


in a deep ditch the waterway is still on ground level, just that the ground is 
lower at this point than it is in the surroundings. 

I would advocate for adding layer=1 to the bridges and leave the waterway 
without layer tag

cheers,
Martin
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[André Pirard]

Hi,

I wonder why we make bridges split and split and split the roads.
In reality, bridges are pieces of concrete or stonework at level -1
under an uninterrupted foil of tarmac at level 0.
Or at level 0 if it's understood that the renderer knows what's a bridge.
And the renderer knows, as it draws two thin stripes beside the road.
So, a bridge can be a little way segment overlaying the road.
This lets the routing software ignore the unnecessary complication of
having to account for bridges as part of the route.
This lets the bridge having its own attributes, unrelated to the road,
for example a different name.
This makes obsolete discussions wondering if the bridge must be split in
two because the road changes in the middle.
Etc. etc., all pieces clutch in very neatly.
And BTW, this is similar to tunnel=culvert which is an optional feature
of a bridge and that surprises no one at layer -1.
And now, if we put bridges and culverts at -1, the rivers or streams are
normally at -2.
Tunnels (inside which the road runs) should be segments too, at level +1
or 0.

I have tagged a number of streams and rivers at -2 -1 0 and I find it
appreciable to have an instant view of where the complete main stream
is, if not exaggeratedly long, as well as less prone to errors.

Cheers,

André.



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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Martin Koppenhoefer]

> Am 14/mar/2014 um 15:51 schrieb Fernando Trebien :
> 
> Do you agree that the river can be tagged with layer=-1 as long as
> this value is correct in relation to the layer of other
> nearby/crossing ways?


I would discourage you to do so. Layer tags should only be applied to ways that 
actually cross other objects on different layers (ie without intersecting them).

To me the Josm way of warning seems correct, as a crossing of objects on 
different layers should issue a warning.

Cheers,
Martin
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Sat, Mar 15, 2014 at 01:24:07AM +0200, Ilpo Järvinen wrote:
> On Sat, 15 Mar 2014, Richard Z. wrote:

> > > Therefore, everyone needs now to handle those hardly useful layer 
> > > warnings about trivial cases (and waste their time on "correcting" them). 
> > 
> > even worse, people just apply layer=-1 to thousands of miles of rivers and
> > similar tricks to hide those warnings.
> 
> Which proves my point. The mappers didn't like the unnecessary burden
> nor the warnings which do in no way improve quality but only reduce 
> signal-to-noise of the validator.

I am in favor of having the warnings fully configurable. Obviously if you
do not know an area well you can't decide whether a waterway crossing should 
be a bridge, culvert or a ford and should not be bothered with such warnings.
And I am thinking this warning should be off by default because it is one
of the most frequently useless warnings that I know.

File tickets for the JOSM validator whenever you think the validator could 
be improved or otherwise fine tuned.

Other warnings otoh should be added. There are many instances of tunnel=culvert
without a layer and almost all of them were accidental errors - someone added
the culvert to the wrong segment of the way.

As of the bridges, the editing software could make it a lot easier to create 
them. Currently its quite many manual steps to insert a bridge properly and 
I think there would be a demand to have a plugin or whatever doing it easier.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Sat, 15 Mar 2014, Richard Z. wrote:

> On Sat, Mar 15, 2014 at 12:30:30AM +0200, Ilpo Järvinen wrote:
> > On Fri, 14 Mar 2014, Richard Z. wrote:
> > 
> > > On Fri, Mar 14, 2014 at 10:34:41PM +0200, Ilpo Järvinen wrote:
> > > > On Fri, 14 Mar 2014, Richard Z. wrote:
> > > > 
> > > > > On Fri, Mar 14, 2014 at 04:51:18PM +0100, Pieren wrote:
> > > > > > On Fri, Mar 14, 2014 at 4:45 PM, Richard Z.  
> > > > > > wrote:
> > > > > 
> > > > > There has been a proposal long ago for bridges to have implicit an 
> > > > > layer
> > > > > and it was not accepted.
> > > > 
> > > > Was that for bridges being equal to layer=1 (which would obviously be 
> > > > bad 
> > > > assumption) or for less than what layer tag can specify (e.g. +/-0.1 
> > > > for 
> > > > bridges/tunnels or whatever < 1)?
> > > 
> > > https://wiki.openstreetmap.org/wiki/Proposed_features/default_layer_for_bridge_and_tunnel
> > 
> > Sadly the mapper point of view is almost totally missing from that 
> > discussion. I've understood that is to most valuable resourse we've and
> > we should try to avoid putting any unnecessary burden on them.
> 
> The proposal had the unfortunate side effect that it would have modified 
> existing crossings in somehwat unpredictable ways.
> If it can be done without that side effect it may be possible.

It's true only if implicit layer equals to layer=1 but not if it would be 
less than that.

> > Therefore, everyone needs now to handle those hardly useful layer 
> > warnings about trivial cases (and waste their time on "correcting" them). 
> 
> even worse, people just apply layer=-1 to thousands of miles of rivers and
> similar tricks to hide those warnings.

Which proves my point. The mappers didn't like the unnecessary burden
nor the warnings which do in no way improve quality but only reduce 
signal-to-noise of the validator.

> > And in fact, I've wasted some time just on that today while what I'm 
> > really after is real geometry errors whose fixing would be much much more 
> > benefial but JOSM validator did not differentiate these two cases for me 
> > but follows such a bad spec.
> 
> what kind of geometry problems?

JOSM validator reports them as:

"Crossing ways" ... many are real issues such as missing nodes or crazy 
geometry in few of the ways (for variaous reasons: redaction bot, 
accidential move in GUI, misclick too far away from one of the ways, etc.) 
but sadly also these bridge/tunnel cases appear as noise in the error 
listing.

(I needed to load lots of highways few weeks ago and I'm still 
processing all those errors a got out from that as a side-product.)

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Sat, Mar 15, 2014 at 12:30:30AM +0200, Ilpo Järvinen wrote:
> On Fri, 14 Mar 2014, Richard Z. wrote:
> 
> > On Fri, Mar 14, 2014 at 10:34:41PM +0200, Ilpo Järvinen wrote:
> > > On Fri, 14 Mar 2014, Richard Z. wrote:
> > > 
> > > > On Fri, Mar 14, 2014 at 04:51:18PM +0100, Pieren wrote:
> > > > > On Fri, Mar 14, 2014 at 4:45 PM, Richard Z.  
> > > > > wrote:
> > > > 
> > > > There has been a proposal long ago for bridges to have implicit an layer
> > > > and it was not accepted.
> > > 
> > > Was that for bridges being equal to layer=1 (which would obviously be bad 
> > > assumption) or for less than what layer tag can specify (e.g. +/-0.1 for 
> > > bridges/tunnels or whatever < 1)?
> > 
> > https://wiki.openstreetmap.org/wiki/Proposed_features/default_layer_for_bridge_and_tunnel
> 
> Sadly the mapper point of view is almost totally missing from that 
> discussion. I've understood that is to most valuable resourse we've and
> we should try to avoid putting any unnecessary burden on them.

The proposal had the unfortunate side effect that it would have modified 
existing
crossings in somehwat unpredictable ways.
If it can be done without that side effect it may be possible.

> Therefore, everyone needs now to handle those hardly useful layer 
> warnings about trivial cases (and waste their time on "correcting" them). 

even worse, people just apply layer=-1 to thousands of miles of rivers and
similar tricks to hide those warnings.

> And in fact, I've wasted some time just on that today while what I'm 
> really after is real geometry errors whose fixing would be much much more 
> benefial but JOSM validator did not differentiate these two cases for me 
> but follows such a bad spec.

what kind of geometry problems?

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Fri, 14 Mar 2014, Richard Z. wrote:

> On Fri, Mar 14, 2014 at 10:34:41PM +0200, Ilpo Järvinen wrote:
> > On Fri, 14 Mar 2014, Richard Z. wrote:
> > 
> > > On Fri, Mar 14, 2014 at 04:51:18PM +0100, Pieren wrote:
> > > > On Fri, Mar 14, 2014 at 4:45 PM, Richard Z.  wrote:
> > > 
> > > There has been a proposal long ago for bridges to have implicit an layer
> > > and it was not accepted.
> > 
> > Was that for bridges being equal to layer=1 (which would obviously be bad 
> > assumption) or for less than what layer tag can specify (e.g. +/-0.1 for 
> > bridges/tunnels or whatever < 1)?
> 
> https://wiki.openstreetmap.org/wiki/Proposed_features/default_layer_for_bridge_and_tunnel

Sadly the mapper point of view is almost totally missing from that 
discussion. I've understood that is to most valuable resourse we've and
we should try to avoid putting any unnecessary burden on them.

Therefore, everyone needs now to handle those hardly useful layer 
warnings about trivial cases (and waste their time on "correcting" them). 
And in fact, I've wasted some time just on that today while what I'm 
really after is real geometry errors whose fixing would be much much more 
benefial but JOSM validator did not differentiate these two cases for me 
but follows such a bad spec.


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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Fri, Mar 14, 2014 at 10:34:41PM +0200, Ilpo Järvinen wrote:
> On Fri, 14 Mar 2014, Richard Z. wrote:
> 
> > On Fri, Mar 14, 2014 at 04:51:18PM +0100, Pieren wrote:
> > > On Fri, Mar 14, 2014 at 4:45 PM, Richard Z.  wrote:
> > 
> > There has been a proposal long ago for bridges to have implicit an layer
> > and it was not accepted.
> 
> Was that for bridges being equal to layer=1 (which would obviously be bad 
> assumption) or for less than what layer tag can specify (e.g. +/-0.1 for 
> bridges/tunnels or whatever < 1)?


https://wiki.openstreetmap.org/wiki/Proposed_features/default_layer_for_bridge_and_tunnel

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Ilpo Järvinen]

On Fri, 14 Mar 2014, Richard Z. wrote:

> On Fri, Mar 14, 2014 at 04:51:18PM +0100, Pieren wrote:
> > On Fri, Mar 14, 2014 at 4:45 PM, Richard Z.  wrote:
> 
> There has been a proposal long ago for bridges to have implicit an layer
> and it was not accepted.

Was that for bridges being equal to layer=1 (which would obviously be bad 
assumption) or for less than what layer tag can specify (e.g. +/-0.1 for 
bridges/tunnels or whatever < 1)?

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Fri, Mar 14, 2014 at 03:55:39PM -0300, Fernando Trebien wrote:
> I don't think you should be required to check the river's layer tag.
> Validators should do this job for you, it's quite easy to write a rule
> for that.

validators can check for many errors but if you want to change
anything you have to understand the whole situation. 
Imagine you want to add a new bridge to a complex freeway intersection
with junctions and overpasses.. the validator will only prevent the
most obvious errors but will give you no clue how to fix them
correctly.
 
> Given two ways that cross internally (excluding connections at
> endpoints), and considering the "layer value" defined explicitly in a
> tag or implicitly 0 when the tag is missing, have the validator issue
> a warning in the following situations:

there is no difference between connections in endpoints or in a crossing 
point as far as I can tell.

> 1. The ways have the same layer value and are unconnected. (They
> should be connected, or else something is surely missing. This could
> actually be considered an "error".)

except for aerial ways and similar exceptions

> 1.1. Also warn if if one way is a waterway and the other is a highway
> and the connection is not explicitly a ford. (It should be, for
> clarity. If it's not, it's also possibly not a ford, therefore the
> connection is wrong.)

there is also the odd case of highways across dams, those are connected
with the waterway

> 2. The ways have different layer values and both are missing a tunnel
> or a bridge tag. (One of them must be either a bridge or a tunnel.
> They can both be tunnels or bridges, but they can't be "none of those
> two" simultaneously in the real world.)

or one of covered,location,indoor,steps,lift or level, maybe more.

> 2.1. Additionally, if one of them is a bridge and the other is a
> tunnel or is neither a tunnel nor a bridge: the bridge should have a
> greater layer value.
> 2.2. Similarly, if one is a tunnel, its layer value should be lower if
> the other is a bridge or has neither tag.

except for indoor mapping and maybe other weird cases.

> These rules apply to any arbitrary combination of stacked waterways
> and highways that I can think of right now. 

also railways?

>  A few examples using two
> overlapping ways:
> 
> a. The ways are connected and do not have a layer tag: everything is
> ok, no rules issue a warning.
> b. The ways are not connected and do not have a layer tag: rule 1
> issues a warning. They must either be connected or lie at different
> layer levels.
> c. The ways are not connected, both have the same layer (say layer=3
> or layer=-4), and have no other tags: rule 1 issues a warning. Similar
> to situation "b".
> d. The ways are not connected and one of them has a layer=-1 tag and
> no other tags: rule 2 issues a warning.

more general: not connected, different layer values and not one of
bridge,tunnel,covered,location,indoor,steps,lift, no level tag and 
a few more things to take into account.

I am not sure it is so easy to catch all that.

> e. The ways are not connected and one of them has a layer=1 tag and no
> other tags: rule 2 issues a warning too.

identical to d?

> f. The ways are not connected, one of them is a bridge with layer=2
> and the other is a tunnel with layer=5: rule 2.1 issues a warning.

unless indoor or other strange cases

> g. The ways are not connected, one of them is a tunnel with layer=1
> and the other is neither a bridge nor has a layer tag (layer=0 is
> assumed): rule 2.2 issues a warning.

 
> Actually, situation "d" is what would discourage people from using
> layer=-1 to work around today's validator warnings. With this ruleset,
> it's impossible to eliminate the warning without actually taking
> action on bridges.

It is a lot easier saying that every bridge and tunnel must have a layer 
tag and enforce that than catching all the situations mentioned in 
situation "d".

With some luck, you can restrict "d" to waterways and it becomes "easy"

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Fri, Mar 14, 2014 at 04:36:26PM +0100, Pieren wrote:
> On Fri, Mar 14, 2014 at 4:15 PM, Jaakko Helleranta.com 
> 
> > At least OsmAnd renders all waterways with layer=-1 with
> > dashed casing, as if they were underground, which to me makes sense
> 
> That's clearly a bug. Waterways underground is specified by "tunnel=*"

this is not a bug. Rivers do not flow through thin air but through areas
which are tagged as landuse=forest, landuse=meadow or some other.

So what happens if you have a river with a layer=-1 going through
a landuse=forest with a layer=0? Quite clearly the river should be
hidden under the forest and my guess is 5 out of 10 renderers do 
exactly that.

Mapnik is way too fault tolerant and works around this obvious breakage.
Maybe it should be changed to be less fault tolerant.

> > So, again : why tag things with with layer= tag when they are essentially on
> > ground level = not above or below other data (or at least natural objects
> > that might be mapped one day *) ? Am I missing something here?
> 
> Real case from real world : a deep ditch where the stream is not
> "underground" but below the "ground" level, is crossing a village
> where we have 10 bridges. Either you add 10 times "layer=1" on the
> bridges or you add 1 time "layer=-1" on the stream.

This is one rare example where it may at first sight appear to be of 
some use. 
However as it is a rare example it will cause more work in the end than 
if you do it the normal way. Nobody expects it being done like this so 
it will cause more thinking for anybody trying to change something 
there.
Everyone who tries to edit it must download the complete data along the 
way that is tagged layer=-1 and understand all crossings there. 
What happens if it is a bigger village or a small town? This does not 
scale well.

This one rare case where it might be of theoretical use is in my opinion
far outweighed by the disadvantages of allowing it:

* prevents validators from doing some very easy and useful checks
* very many people use layer=-1 for waterways incorrectly and taking your
  idea into account would make it much harder to properly detect and fix 
  such errors

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Fernando Trebien]

I don't think you should be required to check the river's layer tag.
Validators should do this job for you, it's quite easy to write a rule
for that. Here's an example:

Given two ways that cross internally (excluding connections at
endpoints), and considering the "layer value" defined explicitly in a
tag or implicitly 0 when the tag is missing, have the validator issue
a warning in the following situations:

1. The ways have the same layer value and are unconnected. (They
should be connected, or else something is surely missing. This could
actually be considered an "error".)
1.1. Also warn if if one way is a waterway and the other is a highway
and the connection is not explicitly a ford. (It should be, for
clarity. If it's not, it's also possibly not a ford, therefore the
connection is wrong.)
2. The ways have different layer values and both are missing a tunnel
or a bridge tag. (One of them must be either a bridge or a tunnel.
They can both be tunnels or bridges, but they can't be "none of those
two" simultaneously in the real world.)
2.1. Additionally, if one of them is a bridge and the other is a
tunnel or is neither a tunnel nor a bridge: the bridge should have a
greater layer value.
2.2. Similarly, if one is a tunnel, its layer value should be lower if
the other is a bridge or has neither tag.

These rules apply to any arbitrary combination of stacked waterways
and highways that I can think of right now. A few examples using two
overlapping ways:

a. The ways are connected and do not have a layer tag: everything is
ok, no rules issue a warning.
b. The ways are not connected and do not have a layer tag: rule 1
issues a warning. They must either be connected or lie at different
layer levels.
c. The ways are not connected, both have the same layer (say layer=3
or layer=-4), and have no other tags: rule 1 issues a warning. Similar
to situation "b".
d. The ways are not connected and one of them has a layer=-1 tag and
no other tags: rule 2 issues a warning.
e. The ways are not connected and one of them has a layer=1 tag and no
other tags: rule 2 issues a warning too.
f. The ways are not connected, one of them is a bridge with layer=2
and the other is a tunnel with layer=5: rule 2.1 issues a warning.
g. The ways are not connected, one of them is a tunnel with layer=1
and the other is neither a bridge nor has a layer tag (layer=0 is
assumed): rule 2.2 issues a warning.

Actually, situation "d" is what would discourage people from using
layer=-1 to work around today's validator warnings. With this ruleset,
it's impossible to eliminate the warning without actually taking
action on bridges.

On Fri, Mar 14, 2014 at 12:48 PM, fly  wrote:
> On 14.03.2014 16:36, Pieren wrote:
>> On Fri, Mar 14, 2014 at 4:15 PM, Jaakko Helleranta.com 
>> 
>>
>>> At least OsmAnd renders all waterways with layer=-1 with
>>> dashed casing, as if they were underground, which to me makes sense
>>
>> That's clearly a bug. Waterways underground is specified by "tunnel=*"
>>
>>> So, again : why tag things with with layer= tag when they are essentially on
>>> ground level = not above or below other data (or at least natural objects
>>> that might be mapped one day *) ? Am I missing something here?
>>
>> Real case from real world : a deep ditch where the stream is not
>> "underground" but below the "ground" level, is crossing a village
>> where we have 10 bridges. Either you add 10 times "layer=1" on the
>> bridges or you add 1 time "layer=-1" on the stream.
>
> Well, I do not get your problem, as bridge/tunnel always need a layer
> tag and you already have to cut the ways to tag the bridge/tunnel, why
> not simply add the layer to the bridge/tunnel and leave everything else
> untouched ?
>
> Using layer tags on long ways is discouraged as you often only need it
> on a small part and it makes it more difficult as you always have to
> check the layer tag of these long ways before adding a new bridge/tunnel
> with appropriate layer value.
>
> cu
> fly
>
>
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Fri, Mar 14, 2014 at 04:51:18PM +0100, Pieren wrote:
> On Fri, Mar 14, 2014 at 4:45 PM, Richard Z.  wrote:
> 
> > in theory yes. However "nearby" is a problem as rivers can be very long.
> > Many people simply tag rivers with layer=-1 without even thinking about
> > the fact that the rivers may now collide with tunnels some hundreds of miles
> > away.
> 
> In general, we should avoid single ways running over hundreds of
> miles. And we have QA tools to detect such issues.

well rivers are thousands of miles long. They don't care about QA tools.

> > Furthermore there is a convention that if there is a crossing with a bridge,
> > the bridge should have the layer tag and not the way bellow it. Similar 
> > tunnel.
> > For both tunnels and bridges layer is now considered mandatory thus it is
> > totally useless to put rivers at layer=-1 unless they are in a tunnel.
> 
> Who decided this and where ? The wiki about bridge says "Bridges
> should have a layer=*, ". "should" is not "must".

it is a polite "must".

There has been a proposal long ago for bridges to have implicit an layer
and it was not accepted.

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Florian Lohoff]

On Fri, Mar 14, 2014 at 04:20:13PM +, Richard Mann wrote:
> Setting the river to layer=-1, and the bridge to layer=0 (or 1) avoids a
> range of rendering artefacts when roads have casings (which they usually
> do). Good practice is only applying that to a shortish section of river,
> obviously.
> 
> I don't know why the wiki has a statement against it - it always seemed
> like a unilateral "I don't like it" from Nathan Edgar the second.

When a bridge is above a river the river stays at layer=0 e.g. no tag or
split at all and the road will get split (you'll need the bridge tag
anyway) together with a layer=1.

So you duplicate the layer=1 tag for every bridge.

Who cares?

Flo
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Fernando Trebien]

I think that adding "layer" to every bridge instead of the river alone
is a wasteful and inefficient approach (takes more time and uses more
database space). IMHO these are much more objective arguments than
simply calling something you disagree with "laziness".

What's wrong with "removing layer=-1" in these cases: it may actually
be semantically correct (as it is in my city: Porto Alegre). All
bridges have been mapped with layer=0 and the river beneath them with
layer=-1. Not a single bridge is missing. (This was checked before
adding the layer tags.)

On Fri, Mar 14, 2014 at 1:06 PM, Florian Lohoff  wrote:
> On Fri, Mar 14, 2014 at 05:01:10PM +0100, Pieren wrote:
>> On Fri, Mar 14, 2014 at 4:48 PM, Richard Z.  wrote:
>>
>> > wiki says that every bridge should have a layer tag. If you are lazy
>> > you can as well omit the layer altogether, it will be still rendered
>> > correctly.
>>
>> It's not a question of laziness. Setting "layer=-1" to the waterway
>> instead of 10 bridges just demonstrates that you understood the
>> original concept of the tag "layer".
>
> Still i feel setting a layer -1 on a waterway and NOT tagging any
> bridges is lazyness. I remove the layer=-1 in those cases and wait
> for keepright to come up with layer violations.
>
> Flo
> --
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>
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Mann]

Setting the river to layer=-1, and the bridge to layer=0 (or 1) avoids a
range of rendering artefacts when roads have casings (which they usually
do). Good practice is only applying that to a shortish section of river,
obviously.

I don't know why the wiki has a statement against it - it always seemed
like a unilateral "I don't like it" from Nathan Edgar the second.
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Florian Lohoff]

On Fri, Mar 14, 2014 at 05:01:10PM +0100, Pieren wrote:
> On Fri, Mar 14, 2014 at 4:48 PM, Richard Z.  wrote:
> 
> > wiki says that every bridge should have a layer tag. If you are lazy
> > you can as well omit the layer altogether, it will be still rendered
> > correctly.
> 
> It's not a question of laziness. Setting "layer=-1" to the waterway
> instead of 10 bridges just demonstrates that you understood the
> original concept of the tag "layer".

Still i feel setting a layer -1 on a waterway and NOT tagging any
bridges is lazyness. I remove the layer=-1 in those cases and wait
for keepright to come up with layer violations.

Flo
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[fly]

On 14.03.2014 16:57, Pieren wrote:
> On Fri, Mar 14, 2014 at 4:48 PM, fly  wrote:
> 
>> Well, I do not get your problem, as bridge/tunnel always need a layer
>> tag and you already have to cut the ways to tag the bridge/tunnel, why
>> not simply add the layer to the bridge/tunnel and leave everything else
>> untouched ?
> 
> You don't see the point where adding one "layer=-1"  is easier than
> adding 10 "layer=1" ? I see the layer tag in "tunnel/bridge" in simple
> cases but you should not follow all recommendations as fixed in stone.

No, as you need to split the river leading to two more objects.

Or do you simply tag the whole way with layer=-1 which is not a good
practices as the next mapper who adds a tunnel has to check the river to
find out that she/he needs to use -2 instead of -1 as value.

cu fly

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Pieren]

On Fri, Mar 14, 2014 at 4:48 PM, Richard Z.  wrote:

> wiki says that every bridge should have a layer tag. If you are lazy
> you can as well omit the layer altogether, it will be still rendered
> correctly.

It's not a question of laziness. Setting "layer=-1" to the waterway
instead of 10 bridges just demonstrates that you understood the
original concept of the tag "layer".

Pieren

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Pieren]

On Fri, Mar 14, 2014 at 4:48 PM, fly  wrote:

> Well, I do not get your problem, as bridge/tunnel always need a layer
> tag and you already have to cut the ways to tag the bridge/tunnel, why
> not simply add the layer to the bridge/tunnel and leave everything else
> untouched ?

You don't see the point where adding one "layer=-1"  is easier than
adding 10 "layer=1" ? I see the layer tag in "tunnel/bridge" in simple
cases but you should not follow all recommendations as fixed in stone.

Pieren

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Pieren]

On Fri, Mar 14, 2014 at 4:45 PM, Richard Z.  wrote:

> in theory yes. However "nearby" is a problem as rivers can be very long.
> Many people simply tag rivers with layer=-1 without even thinking about
> the fact that the rivers may now collide with tunnels some hundreds of miles
> away.

In general, we should avoid single ways running over hundreds of
miles. And we have QA tools to detect such issues.

> Furthermore there is a convention that if there is a crossing with a bridge,
> the bridge should have the layer tag and not the way bellow it. Similar 
> tunnel.
> For both tunnels and bridges layer is now considered mandatory thus it is
> totally useless to put rivers at layer=-1 unless they are in a tunnel.

Who decided this and where ? The wiki about bridge says "Bridges
should have a layer=*, ". "should" is not "must".

Pieren

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Fri, Mar 14, 2014 at 04:36:26PM +0100, Pieren wrote:
> On Fri, Mar 14, 2014 at 4:15 PM, Jaakko Helleranta.com 
> 
> > At least OsmAnd renders all waterways with layer=-1 with
> > dashed casing, as if they were underground, which to me makes sense
> 
> That's clearly a bug. Waterways underground is specified by "tunnel=*"
> 
> > So, again : why tag things with with layer= tag when they are essentially on
> > ground level = not above or below other data (or at least natural objects
> > that might be mapped one day *) ? Am I missing something here?
> 
> Real case from real world : a deep ditch where the stream is not
> "underground" but below the "ground" level, is crossing a village
> where we have 10 bridges. Either you add 10 times "layer=1" on the
> bridges or you add 1 time "layer=-1" on the stream.

wiki says that every bridge should have a layer tag. If you are lazy
you can as well omit the layer altogether, it will be still rendered 
correctly.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[fly]

On 14.03.2014 16:36, Pieren wrote:
> On Fri, Mar 14, 2014 at 4:15 PM, Jaakko Helleranta.com 
> 
>> At least OsmAnd renders all waterways with layer=-1 with
>> dashed casing, as if they were underground, which to me makes sense
> 
> That's clearly a bug. Waterways underground is specified by "tunnel=*"
> 
>> So, again : why tag things with with layer= tag when they are essentially on
>> ground level = not above or below other data (or at least natural objects
>> that might be mapped one day *) ? Am I missing something here?
> 
> Real case from real world : a deep ditch where the stream is not
> "underground" but below the "ground" level, is crossing a village
> where we have 10 bridges. Either you add 10 times "layer=1" on the
> bridges or you add 1 time "layer=-1" on the stream.

Well, I do not get your problem, as bridge/tunnel always need a layer
tag and you already have to cut the ways to tag the bridge/tunnel, why
not simply add the layer to the bridge/tunnel and leave everything else
untouched ?

Using layer tags on long ways is discouraged as you often only need it
on a small part and it makes it more difficult as you always have to
check the layer tag of these long ways before adding a new bridge/tunnel
with appropriate layer value.

cu
fly


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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Richard Z.]

On Fri, Mar 14, 2014 at 11:51:47AM -0300, Fernando Trebien wrote:
> Hello everyone,
> 
> This is a small issue that came up recently in Brazil. In my
> understanding, the layer tag has no specific meaning other than to
> specify a rendering order. The wiki, however, states that it is wrong
> to tag a whole river with layer=-1. The reason for that, as far as I
> could figure, is because current validators (such as JOSM's or
> KeepRight's) will not issue a warning on a waterway x highway crossing
> when their layers are different, leading some users into tagging the
> river with layer=-1 in order to get rid of warnings about missing
> bridges and tunnels. So, I think that the validation rule is
> inadequate: it should warn when a waterway crosses a highway that has
> no bridge or tunnel tag, regardless of the value in the layer tag.
> (Fords are the only exception, AFAIK.)

agree that the error check should be stronger, location, pipeline and covered 
being other exceptions.

> Do you agree that the river can be tagged with layer=-1 as long as
> this value is correct in relation to the layer of other
> nearby/crossing ways?

in theory yes. However "nearby" is a problem as rivers can be very long.

Many people simply tag rivers with layer=-1 without even thinking about
the fact that the rivers may now collide with tunnels some hundreds of miles
away.

Furthermore there is a convention that if there is a crossing with a bridge, 
the bridge should have the layer tag and not the way bellow it. Similar tunnel.

For both tunnels and bridges layer is now considered mandatory thus it is
totally useless to put rivers at layer=-1 unless they are in a tunnel.

Richard

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Fernando Trebien]

"Layer= tag clearly (logically) implies that some data is above or
below some other data. At least to my logic."

>From this logic, layer=-1 means the object is >rendered< beneath
anything that has layer=0 (or, conversely, that anything with layer=0
is rendered on top of anything with layer=-1). It does not mean that
it >is< in fact below it (though it almost always is). That's the
situation of a river passing under a bridge. Likewise, layer=0 means
the object is rendered below anything that has layer=1. Also the same
situation for the situation of a bridge over a river (or of a river
under a bridge). Both approaches should be possible.

"At least OsmAnd renders all waterways with layer=-1 with dashed
casing, as if they were underground, which to me makes sense"

This makes absolutely no sense to me. OsmAnd has confused the concept
of "rendering layer order" with the concept of "level" (underground,
on the ground, above the ground). It may also have confused it with
the concept of a "tunnel", which is rendered using dashed casing in
OSM-Carto (the default map style of the main website).

"I don't understand why anyone would do this. That's it. Why?"

Reason: to avoid having to add a layer tag to every bridge. If a
single river is crossed by 100 bridges, it is easier to add a layer=-1
tag to the river than to add a layer=1 to each of the 100 bridges.

Another reason: to work around the limitations of validators in order
to avoid warnings about "missing bridges". But IMHO, this is the wrong
way to handle the situation, since a workaround is easy AND is
exploited in practice. See here:
http://wiki.openstreetmap.org/wiki/Talk:Key:layer#layer.3D-1_erroneously_used_for_many_italian_rivers

"So, again : why tag things with with layer= tag when they are
essentially on ground level = not above or below other data (or at
least natural objects that might be mapped one day *) ? Am I missing
something here?"

I believe you are missing this: layer=0 does not mean "ground level".
The closest to that idea is level=0, even though it is not always
"ground level" but nearly so almost always. Layer=0 means: "render
this to layer 0". Layer=-1 means: "render this to layer -1", which is
rendered before layer 0, therefore, anything on layer 0 is drawn on
top of things on layer -1.

On Fri, Mar 14, 2014 at 12:15 PM, Jaakko Helleranta.com
 wrote:
> Re; tagging a (complete or longer segment of a) river with layer=-1
>
> I don't understand why anyone would do this. That's it. Why?
>
> Layer= tag clearly (logically) implies that some data is above or below some
> other data. At least to my logic. And I don't seem to be the only one with
> this thinking. At least OsmAnd renders all waterways with layer=-1 with
> dashed casing, as if they were underground, which to me makes sense, but
> what makes all rivers with this unnecessary tag render oddly. There are
> quite a number of such problematic waterways (also) in Nicaragua and Haiti.
>
> So, again : why tag things with with layer= tag when they are essentially on
> ground level = not above or below other data (or at least natural objects
> that might be mapped one day *) ? Am I missing something here?
>
> Cheers,
> -Jaakko
>
> *) I do add layer=1 to all bridges I map even if there wouldn't be any data
> under then at the moment and think that this kind of layer tag use makes
> sense
>
> --
> Sent from my Android device. * +505-8845-3391 * http://about.me/jaakkoh
>
> El mar 14, 2014 8:52 a.m., "Fernando Trebien" 
> escribió:
>>
>> Hello everyone,
>>
>> This is a small issue that came up recently in Brazil. In my
>> understanding, the layer tag has no specific meaning other than to
>> specify a rendering order. The wiki, however, states that it is wrong
>> to tag a whole river with layer=-1. The reason for that, as far as I
>> could figure, is because current validators (such as JOSM's or
>> KeepRight's) will not issue a warning on a waterway x highway crossing
>> when their layers are different, leading some users into tagging the
>> river with layer=-1 in order to get rid of warnings about missing
>> bridges and tunnels. So, I think that the validation rule is
>> inadequate: it should warn when a waterway crosses a highway that has
>> no bridge or tunnel tag, regardless of the value in the layer tag.
>> (Fords are the only exception, AFAIK.)
>>
>> Do you agree that the river can be tagged with layer=-1 as long as
>> this value is correct in relation to the layer of other
>> nearby/crossing ways?
>>
>> --
>> Fernando Trebien
>> +55 (51) 9962-5409
>>
>> "The speed of computer chips doubles every 18 months." (Moore's law)
>> "The speed of software halves every 18 months." (Gates' law)
>>
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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Pieren]

On Fri, Mar 14, 2014 at 4:15 PM, Jaakko Helleranta.com 

> At least OsmAnd renders all waterways with layer=-1 with
> dashed casing, as if they were underground, which to me makes sense

That's clearly a bug. Waterways underground is specified by "tunnel=*"

> So, again : why tag things with with layer= tag when they are essentially on
> ground level = not above or below other data (or at least natural objects
> that might be mapped one day *) ? Am I missing something here?

Real case from real world : a deep ditch where the stream is not
"underground" but below the "ground" level, is crossing a village
where we have 10 bridges. Either you add 10 times "layer=1" on the
bridges or you add 1 time "layer=-1" on the stream.

Pieren

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Re: [Tagging] layer=-1, rivers, bridges and tunnels

[Jaakko Helleranta.com]

Re; tagging a (complete or longer segment of a) river with layer=-1

I don't understand why anyone would do this. That's it. Why?

Layer= tag clearly (logically) implies that some data is above or below
some other data. At least to my logic. And I don't seem to be the only one
with this thinking. At least OsmAnd renders all waterways with layer=-1
with dashed casing, as if they were underground, which to me makes sense,
but what makes all rivers with this unnecessary tag render oddly. There are
quite a number of such problematic waterways (also) in Nicaragua and Haiti.

So, again : why tag things with with layer= tag when they are essentially
on ground level = not above or below other data (or at least natural
objects that might be mapped one day *) ? Am I missing something here?

Cheers,
-Jaakko

*) I do add layer=1 to all bridges I map even if there wouldn't be any data
under then at the moment and think that this kind of layer tag use makes
sense

--
Sent from my Android device. * +505-8845-3391 * http://about.me/jaakkoh
El mar 14, 2014 8:52 a.m., "Fernando Trebien" 
escribió:

> Hello everyone,
>
> This is a small issue that came up recently in Brazil. In my
> understanding, the layer tag has no specific meaning other than to
> specify a rendering order. The wiki, however, states that it is wrong
> to tag a whole river with layer=-1. The reason for that, as far as I
> could figure, is because current validators (such as JOSM's or
> KeepRight's) will not issue a warning on a waterway x highway crossing
> when their layers are different, leading some users into tagging the
> river with layer=-1 in order to get rid of warnings about missing
> bridges and tunnels. So, I think that the validation rule is
> inadequate: it should warn when a waterway crosses a highway that has
> no bridge or tunnel tag, regardless of the value in the layer tag.
> (Fords are the only exception, AFAIK.)
>
> Do you agree that the river can be tagged with layer=-1 as long as
> this value is correct in relation to the layer of other
> nearby/crossing ways?
>
> --
> Fernando Trebien
> +55 (51) 9962-5409
>
> "The speed of computer chips doubles every 18 months." (Moore's law)
> "The speed of software halves every 18 months." (Gates' law)
>
> ___
> Tagging mailing list
> Tagging@openstreetmap.org
> https://lists.openstreetmap.org/listinfo/tagging
>
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[Tagging] layer=-1, rivers, bridges and tunnels

[Fernando Trebien]

Hello everyone,

This is a small issue that came up recently in Brazil. In my
understanding, the layer tag has no specific meaning other than to
specify a rendering order. The wiki, however, states that it is wrong
to tag a whole river with layer=-1. The reason for that, as far as I
could figure, is because current validators (such as JOSM's or
KeepRight's) will not issue a warning on a waterway x highway crossing
when their layers are different, leading some users into tagging the
river with layer=-1 in order to get rid of warnings about missing
bridges and tunnels. So, I think that the validation rule is
inadequate: it should warn when a waterway crosses a highway that has
no bridge or tunnel tag, regardless of the value in the layer tag.
(Fords are the only exception, AFAIK.)

Do you agree that the river can be tagged with layer=-1 as long as
this value is correct in relation to the layer of other
nearby/crossing ways?

-- 
Fernando Trebien
+55 (51) 9962-5409

"The speed of computer chips doubles every 18 months." (Moore's law)
"The speed of software halves every 18 months." (Gates' law)

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