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

Harald Kliems kliems at gmail.com
Thu Apr 3 15:01:57 UTC 2014


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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>
>
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