Another option is to tag water as coastline at places where there is
significant tide. This will include the estuary up until approximately
Quebec City.
Regarding tagging the Great Lakes as coastline: why would there be an
exception for them, where as other large lakes (Great Slave Lake,
Victoria Lake in Africa, Lake Baikal in Russia, etc.) are not? IMO
this can be considered as tagging for the renderer.
A better approach would be to prepare a lowres, generalized dataset
for rendering at low zoomlevels, which only include coastlines and a
couple of large bodies of large water, depending on size. This file
could be updated once a year or so. It is not as if the coastline is
changing so dramatically that it needs to be updated every few weeks.
I think the quality of the current coast lines in OSM is high enough
that this decision could be made, especially with the work Christoph
Hormann has done on Antarctica last year.
Apart from the Great Lakes, this would also mean that the IJsselmeer
in the Netherlands and two lakes in Russia (Ladoga and Onega) need to
be retagged. It might be inconvenient, but why isn't that a problem
for other large lakes?
Regards,
Frank
Quoting [email protected]:
The basic technical restrictions are detailed here
http://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline
It may well be that the person who fixed the coastline (let's call
him Pierre, he's on the list) didn't respect those
conventions/missed a detail/etc and so the change was reverted
pronto to not screw up with the map rendering. Pierre has contacted
the person who reverted him, so we'll know more in a bit.
The question of where does the coastline end and riverbank start is
a question that was probably debated at length 4-5 years ago with no
clear resolution. The page does mention the great lakes as an
example of lakes "wrongly" tagged with coastline, but that will
probably stay like that in the near future. Personally, I think the
great lakes should stay as coastline not just because it'd be hard
to change. It might be worth coming to a consensus here first before
we try to fix the coastline between Montréal and Sorel. Clearly, the
current situation is suboptimal.
My personal approach is to try to consider different definitions,
starting from the one that gives me the eastern most boundary and
then move westward. The options I can identify are:
--all land that is closer to other land than to international waters
is coastline (that gives a boundary somewhere around Nova Scotia and
half-way up Newfoundland)
--Name change boundary: all land that touches water where the
St-lawrence is still called the St-Lawrence is *not* coastline.
(That gives a boundary around the Gaspésie peninsula.)
--Salt to fresh water change. That occurs where the Saguenay river
dumps into the St-lawrence. Anything east would be coastline, west
would not.
--Historical navigation: Quebec city (or around Rivière-du-Loup and
Rimouski?) is roughly where boats would get stuck over winter before
we had really good ice breakers.
--West-side name change: coastline extends through the St-lawrence
river up until it's no longer called the St-Lawrence river.
I could see a point for going even further up the St-Lawrence and
including the great lakes, just because of their size, though
"technically" they're lakes.
This is probably a case where science, common language, semantics,
and database theory have trouble.
Charles
Quoting Harald Kliems <[email protected]>:
Just to add to that: The question of coastline versus riverbank is not just
a mapping/geographical question, but also a technical one. Because of the
length and complexity of the coastline and the requirement to render it at
low zoom levels, there is special pre-processing for converting the
coastline data into shapefiles that only happens every couple weeks (at
least that used to be case). You can see the effects of this when between
z4 and z5 the parts of the St. Lawrence that are not tagged with coastline
disappears on the standard map.
Now this doesn't necessarily explain why the coastline ends and restarts,
but it might have something to do with it. I would also suggest contacting
the person who did the revert directly.
Harald.
On Thu, Apr 3, 2014 at 10:40 AM, Adam Martin <[email protected]>wrote:
Charles,
I took a look at the area that you describe and I see what you mean - the
coastline designation disappears around Sorel and reappears just past
Montreal. Looking in the area of the gap, the use of "Coastline" appears to
suddenly switch to "Water" and "Riverbank". The source of the information
also switches, from the NRCAN database to Bing.
I am not aware of a discussion that flagged this area to be left "as-is"
on the map. I am also not sure why someone would be "protecting" the area
from corrections / changes.
However, I believe I can see where the confusion came from (at least
partially). For reference, this is the St. Lawrence River, an enormous
waterway that drains the Great Lakes into the North Atlantic. A river of
this size generally cannot be described accurately with a single line in
the centre of the waterway as it eliminates a vital level of detail of the
surrounding area. So the St. Lawrence needs to be detailed as a water
polygon in order to preserve the shoreline. The problem here is that there
seems to be some confusion as to what sort of shoreline this represents -
coastline or riverbank. The answer to that is rather complex - where
exactly does the St. Lawrence River stop being a river and become part of
the eastern coast of Canada? The switch between descriptions here appears
to be part of someones attempt to "correct" the designation of the
shoreline in the river for an area that they consider to be part of the
"River" that is the St. Lawrence (as opposed to the coastline that the
river drains into).
I think the question here is the same - where does the St. Lawrence stop
being a river and start being a part of the coastline?
Adam
On Wed, Apr 2, 2014 at 10:10 PM, Charles Basenga Kiyanda <
[email protected]> wrote:
Anybody know why the coastline stops about midway along the Montreal
Island (and also Ile Jésus) and then starts again around Sorel? I got one
report from someone who tried to fix this and was quickly reverted. Should
it be fixed at some point and it's just such a large undertaking that
nobody is willing to do it yet or was there a discussion and subsequent
consensus to adopt the current state of the coastline?
Thanks,
Charles
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