Re: [Tagging] Coastal beach definition for mapping.

[Warin]

I think it best to change the wiki beach front page.

At the moment only one method is mentioned ... and that is from the hi 
tide and away from the water.
I think the other method - from the low tide and away from the water 
should be stated too.


 - On 04/04/18 20:58, Dave Swarthout wrote:
This is an interesting problem but it has no easy solution. Even if 
the Wiki definition was clear, unless you happen to be able to measure 
or otherwise determine the "mean high tide" line and other important 
characteristics, what we map as beach or tidal flat is purely an 
approximation, especially in areas having a large tidal range, as in 
Alaska where I do the bulk of my mapping (20-30 feet). Satellite 
imagery may offer a clear vision of beach and tidal flat but we cannot 
determine the height of the tide when the photo was obtained. 
Was it at high tide, low tide, or somewhere in between?


I agree that a beach is a place where wave action has created a 
relatively steep slope. Other areas closer to the sea are flatter and 
are often composed of finer particles, fine sand and clay, often 
referred to as mud. Indeed, much of Alaska's coastline could be 
characterized as mud_flat due to the large amount of solids Alaskan 
rivers transport to the ocean. In my hometown of Homer, Alaska, spring 
low tides can be so extreme that the water beyond the mud_flat is too 
distant to see. What you can see is mud, lots of it.


Taginfo tells us that neither mud_flat or tidal_flat (or variations 
without the underscore separator) are much in use, however, for some 
of my mapping I've used the combination

natural=wetland
wetland=tidalflat (but it could just as easily be wetland=mudflat)

I've drawn those areas the best I can based on convenient satellite 
imagery knowing full well it's merely a rough approximation. There may 
not be a better solution.


Cheers,
Dave

On Wed, Apr 4, 2018 at 4:53 PM, Warin <61sundow...@gmail.com 
> wrote:


On 04/04/18 18:18, Christoph Hormann wrote:

On Wednesday 04 April 2018, Warin wrote:

So a 'beach' may include a 'tidal flat' ... confused.

I tried to explain the difference - a beach is primarily
shaped by waves
while a tidal flat is shaped by tidal currents.

The domination of waves can usually be seen in the form of a
smooth
surface where structures (like waves in the slope) typically form
parallel to the shore.  Like here:

https://commons.wikimedia.org/wiki/File:The_beach_1.JPG


On tidal flats OTOH the water flow often form small or large
channels
like here:


https://commons.wikimedia.org/wiki/File:Waikaraka_Cycleway_from_Mangere_Bridge_IV.jpg



Beaches can only form from relatively coarse material (sand or
coarser) - fine silt cannot form beaches because it does not
settle
fast enough in the fast moving water so the beach would
quickly erode
away.  Tidal flats can form both from fine silt and coarse sand.

At coasts with a significant tidal range (like in the UK)
there is often
a beach in the upper part of the tidal range with a steeper
slope and
coarse sand and a tidal flat with less slope with either sand
as well
or finer material.

Example:


https://mc.bbbike.org/mc/?lon=-4.390229=51.716636=14=3=bing-satellite=mapnik=google-satellite




That is a very nice example, thanks  I'd call them 'mud flats'
... :)

Broome, Western Australia has tides of ~10 meters  and is know for
the 'Staircase to the Moon Festival'
where the moon is reflected off the beach/tidal flats ripples to
form a stair case up to the moon, very pretty ...
But I'm not certain if that is a tidal flat area or not ... the
imagery does not revel it ..


https://mc.bbbike.org/mc/?lon=-4.390229=51.716636=14=3=bing-satellite=mapnik=google-satellite



Arrr the visitors centre says tidal flats ..
http://www.visitbroome.com.au/discover/facts-figures/staircase-to-the-moon

There are better photos of the staircase ..
http://jksj.org/2015/06/10/broome/


I'd still map the sand area as the beach as seen in the imagery,
think the 'tidal flat' would have one edge as the beach edge and
the rest be further out to sea.





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Re: [Tagging] Coastal beach definition for mapping.

[Christoph Hormann]

On Wednesday 04 April 2018, Malcolm Herring wrote:
> > It seems some mappers go to the extreme opposite and map the
> > coastline across the mouth of an estuary that is clearly part of
> > the ocean:
> >
> > 
>
> Many ocean/river boundaries are not arbitrary, but reflect official
> boundaries where a coastal authority's water ends and a river
> authority's water begins.

There is no such thing as an ocean/river boundary - there are political 
boundaries and there are limits of physical geography features.  When 
mappers align geometries of physical geography features (like 
natural=water, waterway=riverbank or natural=coastline) to 
administrative boundaries or baselines that is always wrong and is 
usually done to communicate a certain non-verifiable view of the 
physical reality to underline certain political goals - in case of the 
Rio de la Plata this is the aim to defend the claims Argentina and 
Uruguay make regarding the limits of their territorial waters (which 
are internationally disputed):

http://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1790=nrj
https://www.state.gov/documents/organization/57675.pdf

Independent of that the placement of the coastline at river mouths is 
generally somewhat variable.  I wrote a proposal a few years back aimed 
at defining some verifiable limits for that:

https://wiki.openstreetmap.org/wiki/Proposed_Features/Coastline-River_transit_placement

-- 
Christoph Hormann
http://www.imagico.de/

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Re: [Tagging] Coastal beach definition for mapping.

[Derya Dilmen (Insight Global Inc)]

Thank you much, that is me who did it, my mistake, I was trying to cover a 
coastline for the marine structures, the boundaries were following the same 
coastline and there was an island inside the estuary that the coastline was 
defined.

https://www.openstreetmap.org/#map=15/-33.6465/151.2835



-Original Message-
From: Malcolm Herring [mailto:malcolm.herr...@btinternet.com] 
Sent: Wednesday, April 4, 2018 9:15 AM
To: tagging@openstreetmap.org
Subject: Re: [Tagging] Coastal beach definition for mapping.

On 04/04/2018 12:40, Eugene Alvin Villar wrote:
> It seems some mappers go to the extreme opposite and map the coastline 
> across the mouth of an estuary that is clearly part of the ocean:
> 
> <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.
> openstreetmap.org%2Fway%2F186710973=02%7C01%7Cv-dedilm%40microsof
> t.com%7C9be8454d51d04876525808d59a479ea0%7C72f988bf86f141af91ab2d7cd01
> 1db47%7C1%7C0%7C636584554761019595=pz351Prv1unpcfyM3cgLSV6m6dtTE
> WVfF1dFNeBbLYE%3D=0>

Many ocean/river boundaries are not arbitrary, but reflect official boundaries 
where a coastal authority's water ends and a river authority's water begins.


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Re: [Tagging] Coastal beach definition for mapping.

[Malcolm Herring]

On 04/04/2018 12:40, Eugene Alvin Villar wrote:
It seems some mappers go to the extreme opposite and map the coastline 
across the mouth of an estuary that is clearly part of the ocean:





Many ocean/river boundaries are not arbitrary, but reflect official 
boundaries where a coastal authority's water ends and a river 
authority's water begins.



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Re: [Tagging] Coastal beach definition for mapping.

[Kevin Kenny]

On Wed, Apr 4, 2018 at 7:40 AM, Eugene Alvin Villar  wrote:
> On Tue, Apr 3, 2018 at 9:22 PM, Martin Koppenhoefer 
> wrote:
>>u
>> the coastline should represent the limit of the sea, in case of a river
>> flowing in, people look at the level of salt in the water and whether the
>> level of the river is influenced by tides (afaik)
>
>
> It seems some mappers go to the extreme opposite and map the coastline
> across the mouth of an estuary that is clearly part of the ocean:
>
> https://www.openstreetmap.org/way/186710973

How something is called and thought of by the locals is also taken into account.

Example: The Hudson River is hard to draw a firm boundary on. If one
were to take the position that "any shoreline with a measurable tide
is part of the coastline," then the coastline extends all the way up
to the Federal Dam in Troy, New York:
https://www.openstreetmap.org/way/90929525

It's still obviously a river up there. The water is fresh, and flows
quite strongly in one direction. (When the tide is rising, it flows a
little less strongly. It never reverses.)

Drawing the salt front would be ambiguous by tens of km. In a wet
season, its a highly diffuse front near the entrance to the Tappan Zee
(note to self: make a relation for the waterbody!)
https://www.openstreetmap.org/way/318106482 but in a drought it can
retreat as far as the Poughkeepsie Bridge
https://www.openstreetmap.org/way/24185107 or even farther. Even where
it's brackish, it's still called a 'river,' and if you said that it
was 'coastline,' the locals would look at you as if you had two heads.

People seem to agree that the piers in Manhattan where the big ships
dock are on the coast, so the line is drawn somewhat arbitrarily north
of Spuyten Duyvil https://www.openstreetmap.org/way/135719690.

I'm not going to say that the local mappers are wrong, even though the
estuary is deep enough that vessels of considerable draft can sail
into Albany. There's a WW2-vintage destroyer moored there on
more-or-less permanent display. She got there under her own steam. In
historic times, the Albany riverfront would display a small forest of
ships' masts - but it's always been called a riverport, not a seaport.
A sailing vessel would have to kedge the faster sections of the river.
I pity those who had to man the capstan.

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Re: [Tagging] Coastal beach definition for mapping.

[Dave Swarthout]

 Eugene Alvin Villar  wrote:
It seems some mappers go to the extreme opposite and map the coastline
across the mouth of an estuary that is clearly part of the ocean:

Yes, they do this because it's fast and they may have other more pressing
issues to deal with at the moment. It's also non-controversial in the sense
that it's not actually "wrong", it's merely inaccurate. Someone with more
time or motivation can come in later to do it more thoroughly.

On Wed, Apr 4, 2018 at 6:40 PM, Eugene Alvin Villar 
wrote:

> On Tue, Apr 3, 2018 at 9:22 PM, Martin Koppenhoefer <
> dieterdre...@gmail.com> wrote:
>
>> the coastline should represent the limit of the sea, in case of a river
>> flowing in, people look at the level of salt in the water and whether the
>> level of the river is influenced by tides (afaik)
>>
>
> It seems some mappers go to the extreme opposite and map the coastline
> across the mouth of an estuary that is clearly part of the ocean:
>
> https://www.openstreetmap.org/way/186710973
>
>
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>
>


-- 
Dave Swarthout
Homer, Alaska
Chiang Mai, Thailand
Travel Blog at http://dswarthout.blogspot.com
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Re: [Tagging] Coastal beach definition for mapping.

[Eugene Alvin Villar]

On Tue, Apr 3, 2018 at 9:22 PM, Martin Koppenhoefer 
wrote:

> the coastline should represent the limit of the sea, in case of a river
> flowing in, people look at the level of salt in the water and whether the
> level of the river is influenced by tides (afaik)
>

It seems some mappers go to the extreme opposite and map the coastline
across the mouth of an estuary that is clearly part of the ocean:

https://www.openstreetmap.org/way/186710973
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Re: [Tagging] Coastal beach definition for mapping.

[Dave Swarthout]

This is an interesting problem but it has no easy solution. Even if the
Wiki definition was clear, unless you happen to be able to measure or
otherwise determine the "mean high tide" line and other important
characteristics, what we map as beach or tidal flat is purely an
approximation, especially in areas having a large tidal range, as in Alaska
where I do the bulk of my mapping (20-30 feet). Satellite imagery may offer
a clear vision of beach and tidal flat but we cannot determine the height
of the tide when the photo was obtained. Was it at high tide, low tide, or
somewhere in between?

I agree that a beach is a place where wave action has created a relatively
steep slope. Other areas closer to the sea are flatter and are often
composed of finer particles, fine sand and clay, often referred to as mud.
Indeed, much of Alaska's coastline could be characterized as mud_flat due
to the large amount of solids Alaskan rivers transport to the ocean. In my
hometown of Homer, Alaska, spring low tides can be so extreme that the
water beyond the mud_flat is too distant to see. What you can see is mud,
lots of it.

Taginfo tells us that neither mud_flat or tidal_flat (or variations without
the underscore separator) are much in use, however, for some of my mapping
I've used the combination
natural=wetland
wetland=tidalflat (but it could just as easily be wetland=mudflat)

I've drawn those areas the best I can based on convenient satellite imagery
knowing full well it's merely a rough approximation. There may not be a
better solution.

Cheers,
Dave

On Wed, Apr 4, 2018 at 4:53 PM, Warin <61sundow...@gmail.com> wrote:

> On 04/04/18 18:18, Christoph Hormann wrote:
>
>> On Wednesday 04 April 2018, Warin wrote:
>>
>>> So a 'beach' may include a 'tidal flat' ... confused.
>>>
>> I tried to explain the difference - a beach is primarily shaped by waves
>> while a tidal flat is shaped by tidal currents.
>>
>> The domination of waves can usually be seen in the form of a smooth
>> surface where structures (like waves in the slope) typically form
>> parallel to the shore.  Like here:
>>
>> https://commons.wikimedia.org/wiki/File:The_beach_1.JPG
>>
>> On tidal flats OTOH the water flow often form small or large channels
>> like here:
>>
>> https://commons.wikimedia.org/wiki/File:Waikaraka_Cycleway_f
>> rom_Mangere_Bridge_IV.jpg
>>
>> Beaches can only form from relatively coarse material (sand or
>> coarser) - fine silt cannot form beaches because it does not settle
>> fast enough in the fast moving water so the beach would quickly erode
>> away.  Tidal flats can form both from fine silt and coarse sand.
>>
>> At coasts with a significant tidal range (like in the UK) there is often
>> a beach in the upper part of the tidal range with a steeper slope and
>> coarse sand and a tidal flat with less slope with either sand as well
>> or finer material.
>>
>> Example:
>>
>> https://mc.bbbike.org/mc/?lon=-4.390229=51.716636=1
>> 4=3=bing-satellite=mapnik=google-satellite
>>
>
> That is a very nice example, thanks  I'd call them 'mud flats' ... :)
>
> Broome, Western Australia has tides of ~10 meters  and is know for the
> 'Staircase to the Moon Festival'
> where the moon is reflected off the beach/tidal flats ripples to form a
> stair case up to the moon, very pretty ...
> But I'm not certain if that is a tidal flat area or not ... the imagery
> does not revel it ..
>
> https://mc.bbbike.org/mc/?lon=-4.390229=51.716636=1
> 4=3=bing-satellite=mapnik=google-satellite
>
> Arrr the visitors centre says tidal flats ..
> http://www.visitbroome.com.au/discover/facts-figures/staircase-to-the-moon
> There are better photos of the staircase .. http://jksj.org/2015/06/10/bro
> ome/
>
> I'd still map the sand area as the beach as seen in the imagery,
> think the 'tidal flat' would have one edge as the beach edge and the rest
> be further out to sea.
>
>
>
>
>
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-- 
Dave Swarthout
Homer, Alaska
Chiang Mai, Thailand
Travel Blog at http://dswarthout.blogspot.com
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Re: [Tagging] Coastal beach definition for mapping.

[Warin]

On 04/04/18 18:18, Christoph Hormann wrote:

On Wednesday 04 April 2018, Warin wrote:

So a 'beach' may include a 'tidal flat' ... confused.

I tried to explain the difference - a beach is primarily shaped by waves
while a tidal flat is shaped by tidal currents.

The domination of waves can usually be seen in the form of a smooth
surface where structures (like waves in the slope) typically form
parallel to the shore.  Like here:

https://commons.wikimedia.org/wiki/File:The_beach_1.JPG

On tidal flats OTOH the water flow often form small or large channels
like here:

https://commons.wikimedia.org/wiki/File:Waikaraka_Cycleway_from_Mangere_Bridge_IV.jpg

Beaches can only form from relatively coarse material (sand or
coarser) - fine silt cannot form beaches because it does not settle
fast enough in the fast moving water so the beach would quickly erode
away.  Tidal flats can form both from fine silt and coarse sand.

At coasts with a significant tidal range (like in the UK) there is often
a beach in the upper part of the tidal range with a steeper slope and
coarse sand and a tidal flat with less slope with either sand as well
or finer material.

Example:

https://mc.bbbike.org/mc/?lon=-4.390229=51.716636=14=3=bing-satellite=mapnik=google-satellite


That is a very nice example, thanks  I'd call them 'mud flats' ... :)

Broome, Western Australia has tides of ~10 meters  and is know for the 
'Staircase to the Moon Festival'
where the moon is reflected off the beach/tidal flats ripples to form a stair 
case up to the moon, very pretty ...
But I'm not certain if that is a tidal flat area or not ... the imagery does 
not revel it ..

https://mc.bbbike.org/mc/?lon=-4.390229=51.716636=14=3=bing-satellite=mapnik=google-satellite

Arrr the visitors centre says tidal flats ..
http://www.visitbroome.com.au/discover/facts-figures/staircase-to-the-moon
There are better photos of the staircase .. http://jksj.org/2015/06/10/broome/

I'd still map the sand area as the beach as seen in the imagery,
think the 'tidal flat' would have one edge as the beach edge and the rest be 
further out to sea.




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Re: [Tagging] Coastal beach definition for mapping.

[Christoph Hormann]

On Wednesday 04 April 2018, Warin wrote:
>
> So a 'beach' may include a 'tidal flat' ... confused.

I tried to explain the difference - a beach is primarily shaped by waves 
while a tidal flat is shaped by tidal currents.

The domination of waves can usually be seen in the form of a smooth 
surface where structures (like waves in the slope) typically form 
parallel to the shore.  Like here:

https://commons.wikimedia.org/wiki/File:The_beach_1.JPG

On tidal flats OTOH the water flow often form small or large channels 
like here:

https://commons.wikimedia.org/wiki/File:Waikaraka_Cycleway_from_Mangere_Bridge_IV.jpg

Beaches can only form from relatively coarse material (sand or 
coarser) - fine silt cannot form beaches because it does not settle 
fast enough in the fast moving water so the beach would quickly erode 
away.  Tidal flats can form both from fine silt and coarse sand.

At coasts with a significant tidal range (like in the UK) there is often 
a beach in the upper part of the tidal range with a steeper slope and 
coarse sand and a tidal flat with less slope with either sand as well 
or finer material.

Example:

https://mc.bbbike.org/mc/?lon=-4.390229=51.716636=14=3=bing-satellite=mapnik=google-satellite

In the upper part this is clearly a beach (as visible in the Bing image 
with high water level).  In the lower part with the tidal channels 
visible in the Google image it is clearly a tidal flat.

-- 
Christoph Hormann
http://www.imagico.de/

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Re: [Tagging] Coastal beach definition for mapping.

[Warin]

On 04/04/18 07:56, Warin wrote:

On 03/04/18 18:32, Christoph Hormann wrote:

On Monday 02 April 2018, Warin wrote:

The present OSM wiki defintion for beach

is "Coastal beaches should be mapped down to the mean high water
spring line (natural
=coastline
)"

(from https://wiki.openstreetmap.org/wiki/Tag:natural=beach)

I think this is incorrect .. they should be mapped past the high
water mark to the low water mark.

This has been a disputed subject for a long time.  In any case the wiki
clearly does not reflect the current use of the tag here though.  The
following situations exist frequently in reality:

a) coast at high water line, beach only above high water line. This
leads to very narrow beaches since the area correctly to be tagged as a
beach is only between the regular high water line and the extreme
(storm flood) high water line.

b) coast at high water line, beach down to lower end of beach (either
the low water line or the transit of the beach to a tidal flat -
sometimes, in particular in the UK, the tidal flat is also incorrectly
tagged natural=beach).

c) coast at an intermediate water level (the level shown in whatever
image is used), beach ends at this water level (i.e. mappers directly
draw what they see in the image).

All variants are common, (a) in my experience is not more common than
(b).

For clarity regarding the difference between beaches and tidal flats:  A
beach is formed by waves, it therefore always has a significant slope
and is rarely wider than a few hundred meters.  A tidal flat is a flat
area exposed at low tide that is shaped by the tidal currents.


Thanks Christoph, had not considered 'tidal flats'...
there are some large areas I know of ...
was thinking about them while I considered 'beaches', but had not 
considered the term 'tidal flats'.




Humm tidal flats are sometimes called 'mud flats' ...
Came across this from the US Army https://definedterm.com/a/document/10633
tidal flats - (1) _Marsh _y 
or muddy areas covered and uncovered by the rise and fall of the _tide 
_. A TIDAL MARSH. (2) _Marsh 
_y or muddy areas of the 
seabed which are covered and uncovered by the rise and fall of tidal water.


beach - The zone of _unconsolidated 
_ material that extends 
landward from the _low water line 
_ to the place where there 
is marked change in material or physiographic form, or to the line of 
permanent vegetation (usually the effective limit of storm _wave 
_s). The seaward limit of a 
beach--unless otherwise specified--is the mean _low water line 
_. A beach includes 
_foreshore _ and _backshore 
_. (See Figure A-1) See also 
SHORE, SUSTAINABLE BEACH, and SELF-SUSTAINING BEACH, and TIDELANDS.


So a 'beach' may include a 'tidal flat' ... confused.


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Re: [Tagging] Coastal beach definition for mapping.

[Warin]

On 03/04/18 23:22, Martin Koppenhoefer wrote:



sent from a phone

On 2. Apr 2018, at 23:40, Graeme Fitzpatrick > wrote:


Should it continue more or less straight, following the line of the 
beach, across the mouth of the estuary; or should it follow the 
estuary / river bank for an undetermined distance inland?



the coastline should represent the limit of the sea, in case of a 
river flowing in, people look at the level of salt in the water and 
whether the level of the river is influenced by tides (afaik), for 
example here you can see a coastline at a “river”:


https://www.openstreetmap.org/way/88960837#map=9/53.6926/9.3947


River flows can be extremely different from one season to the next in 
some parts of the world.
Consider the tropics where the major seasons are described as 'wet' and 
'dry', river levels can change by 5 meters between the seasons.


In other places the tide can influence river levels for many kilometres 
inland.


In both those cases the salt levels will vary from one extreme to another.

Possibly best to take the minimum intrusion of the sea into the river? 
Maybe not for some though - the rate of flow will have fresh water going 
out into what most would call the sea!


Where this detail is unknown then Graeme's approach of a straight line 
across the mouth of the river can be used to minimise work and signify 
the lack of information or the conflict for the area.
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Re: [Tagging] Coastal beach definition for mapping.

[Warin]

On 03/04/18 18:32, Christoph Hormann wrote:

On Monday 02 April 2018, Warin wrote:

The present OSM wiki defintion for beach

is "Coastal beaches should be mapped down to the mean high water
spring line (natural
=coastline
)"

(from https://wiki.openstreetmap.org/wiki/Tag:natural=beach)

I think this is incorrect .. they should be mapped past the high
water mark to the low water mark.

This has been a disputed subject for a long time.  In any case the wiki
clearly does not reflect the current use of the tag here though.  The
following situations exist frequently in reality:

a) coast at high water line, beach only above high water line.  This
leads to very narrow beaches since the area correctly to be tagged as a
beach is only between the regular high water line and the extreme
(storm flood) high water line.

b) coast at high water line, beach down to lower end of beach (either
the low water line or the transit of the beach to a tidal flat -
sometimes, in particular in the UK, the tidal flat is also incorrectly
tagged natural=beach).

c) coast at an intermediate water level (the level shown in whatever
image is used), beach ends at this water level (i.e. mappers directly
draw what they see in the image).

All variants are common, (a) in my experience is not more common than
(b).

For clarity regarding the difference between beaches and tidal flats:  A
beach is formed by waves, it therefore always has a significant slope
and is rarely wider than a few hundred meters.  A tidal flat is a flat
area exposed at low tide that is shaped by the tidal currents.


Thanks Christoph, had not considered 'tidal flats'...
there are some large areas I know of ...
was thinking about them while I considered 'beaches', but had not considered 
the term 'tidal flats'.


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Re: [Tagging] Coastal beach definition for mapping.

[Martin Koppenhoefer]

sent from a phone

> On 2. Apr 2018, at 23:40, Graeme Fitzpatrick  wrote:
> 
> Should it continue more or less straight, following the line of the beach, 
> across the mouth of the estuary; or should it follow the estuary / river bank 
> for an undetermined distance inland?


the coastline should represent the limit of the sea, in case of a river flowing 
in, people look at the level of salt in the water and whether the level of the 
river is influenced by tides (afaik), for example here you can see a coastline 
at a “river”:

https://www.openstreetmap.org/way/88960837#map=9/53.6926/9.3947


Cheers,
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Re: [Tagging] Coastal beach definition for mapping.

[Christoph Hormann]

On Monday 02 April 2018, Warin wrote:
> The present OSM wiki defintion for beach
>
> is "Coastal beaches should be mapped down to the mean high water
> spring line (natural
> =coastline
> )"
>
> (from https://wiki.openstreetmap.org/wiki/Tag:natural=beach)
>
> I think this is incorrect .. they should be mapped past the high
> water mark to the low water mark.

This has been a disputed subject for a long time.  In any case the wiki 
clearly does not reflect the current use of the tag here though.  The 
following situations exist frequently in reality:

a) coast at high water line, beach only above high water line.  This 
leads to very narrow beaches since the area correctly to be tagged as a 
beach is only between the regular high water line and the extreme 
(storm flood) high water line.

b) coast at high water line, beach down to lower end of beach (either 
the low water line or the transit of the beach to a tidal flat - 
sometimes, in particular in the UK, the tidal flat is also incorrectly 
tagged natural=beach).

c) coast at an intermediate water level (the level shown in whatever 
image is used), beach ends at this water level (i.e. mappers directly 
draw what they see in the image).

All variants are common, (a) in my experience is not more common than 
(b).

For clarity regarding the difference between beaches and tidal flats:  A 
beach is formed by waves, it therefore always has a significant slope 
and is rarely wider than a few hundred meters.  A tidal flat is a flat 
area exposed at low tide that is shaped by the tidal currents.

-- 
Christoph Hormann
http://www.imagico.de/

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Re: [Tagging] Coastal beach definition for mapping.

[Warin]

On 03/04/18 05:27, Martin Koppenhoefer wrote:


sent from a phone


On 2. Apr 2018, at 06:13, Warin <61sundow...@gmail.com> wrote:

Comments? Any that support the high water mark limit I'd be interested in 
seeing.


I find it generally difficult to estimate high and low water positions, when 
I’m adding beaches at the sea I will usually use the coastline as border 
towards the water and the put the rear border where it looks like the end of 
the beach. On rivers and lakes I would also use the water boundary as border 
for the beach.



Where is it difficult? An example would help?

As a counter example;

Here is Bondi Beach, Australia. 
https://www.openstreetmap.org/edit#map=17/-33.89168/151.27720

If you use the LPI Imagery you can clearly see the sand under the water edge.

If you use the Bing, Digital Globe, ERSI, Mapbox, AGRI imagery you can see 
towards the low water mark.




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Re: [Tagging] Coastal beach definition for mapping.

[Graeme Fitzpatrick]

On 3 April 2018 at 05:27, Martin Koppenhoefer 
wrote:

>
>
> when I’m adding beaches at the sea I will usually use the coastline as
> border towards the water and the put the rear border where it looks like
> the end of the beach. On rivers and lakes I would also use the water
> boundary as border for the beach.
>

Moving way from high & low tides for a moment to the actual "coastline"
itself.

When you have rivers opening into the sea, where does the "coastline" go?

Should it continue more or less straight, following the line of the beach,
across the mouth of the estuary; or should it follow the estuary / river
bank for an undetermined distance inland?

Just one of any number near us
https://www.openstreetmap.org/edit#map=16/-28.1294/153.4824, the coastline
follows the estuary then river bank for ~5 km's inland (including around 2
canal estates!), then crosses the creek (which at that spot is <10 m's
wide) & returns to the beach.

Wouldn't it make for sense for the coastline to cross from Currumbin Rock
to the tip of the groyne, with the rest of the line being river bank?

Thanks

Graeme
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Re: [Tagging] Coastal beach definition for mapping.

[Martin Koppenhoefer]

sent from a phone

> On 2. Apr 2018, at 06:13, Warin <61sundow...@gmail.com> wrote:
> 
> Comments? Any that support the high water mark limit I'd be interested in 
> seeing.


I find it generally difficult to estimate high and low water positions, when 
I’m adding beaches at the sea I will usually use the coastline as border 
towards the water and the put the rear border where it looks like the end of 
the beach. On rivers and lakes I would also use the water boundary as border 
for the beach.



Cheers,
Martin 
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