[OSM-talk] Mapping rivers that flow into/through lakes?

Maarten Deen mdeen at xs4all.nl
Fri Feb 23 11:04:01 UTC 2018


On 2018-02-23 11:35, Rory McCann wrote:
> On 23/02/18 06:53, Maarten Deen wrote:
>> I see nothing wrong with those examples, I would do it the same, 
>> especially if the rivers can be sailed on by boat. Then you absolutely 
>> need the rivers to be connected to a central river (or fairway) in the 
>> lake.
> 
> But then how far do you go? Should every stream be connected to the
> central river? e.g. what about here (
> http://tools.geofabrik.de/osmi/?view=water&lon=28.57869&lat=-16.75136&zoom=11
> )?

Mappers discretion. I'm not advocating a "must" in this case. I'm saying 
it's not a bad thing if it is done and in some circumstances it is 
preferrable.
See it as roads connecting to a square. As long as routing over areas is 
not commonplace it is acceptable and even preferrable to lay roads over 
the square.

> If some rivers/streams shouldn't be connected, then some data consumers
> will have to do an automatic connection anyway. When measuring water 
> run
> off and pollution, you probably want to know that "stuff going into
> stream X will eventually get to point Y downstream" (right?).

Yes. OSM gets used (maybe misused) for all kinds of purposes, but a 
hydrological analysis would be impossible if streams that are physically 
connected are not so in OSM.

> Connecting all means that large lakes will be full of a "skeleton" of
> joining rivers/streams, and a small 1km stream could get a lot longer.

Good point, but can be solved by using relations for the streams and not 
including the part of the stream that runs through the lake. In any 
case, I would think it strange to still use the the name of the stream 
on the part that runs through the lake.

Maarten



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