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

personal at charleskiyanda.com personal at charleskiyanda.com
Thu Apr 3 16:26:50 UTC 2014


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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>>
>>
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