[Talk-ca] coastline between Montreal and Sorel, Quebec

steggink at steggink.org steggink at steggink.org
Fri Apr 4 06:21:43 UTC 2014

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?



Quoting personal at charleskiyanda.com:

> 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 <kliems at gmail.com>:
>> 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 <s.adam.martin at gmail.com>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 <
>>> personal at charleskiyanda.com> 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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