|Information about watershed relations|
|Tools for this tag|
This page collects all information about watershed relations.
There exists no proposal and no voting about this tagging.
A tag type=watershed got introduced to be able to describe a basin/watershed system of a river. Just adding child relations of tributaries to a parent relation does not get rendered/is not yet implemented/will never be implemented. For now one has to add all single waterway=river of a every single river to a parent river's watershed.
To also add areas (waterway=riverbank or natural=water) to the watershed-relation is not recommended - it would mean unnecessary overhead if there is already the waterway=river tag present in the relation.
History of watershed relations
- 2009-06: user:katpatuka started creating watershed relations to simplify loading watersheds
|type||watershed||type tag of the relation|
|name||name of the watershed / basin|
|parent_basin||name of the parent_basin|
The following members are used in the current osm database:
|None||*||tributary relation with relation type=watershed|
|None||*||tributary waterways with relation type=waterway|
|None||*||any kind of waterway ways. They usually have a waterway=[river, canal, stream, drain, ditch] tag |
no riverbank areas or ways
see also: Taginfo about type=watershed
Do we need relations for watersheds?
Discussions on mailing lists, ...
- Discussion on German Mailing list Talk-de: Braucht es gemappte Flusseinzugsgebiete?
Opinion of user:werner2101
Actually, I think that we don't need watershed relations. They can be created by scanning all upstream waterways starting with a relation:waterway. It is much easier to maintain single waterway relations and let a computer to the rest.
As long as the watershed relations exist, I think we should reuse as much upstream relations as possible and not add simple waterway way segments to the watershed relations.
I think it's a bad idea to mix waterway relations and watershed relations. This mixed mapping method is partly used in france, where tributaries of waterway relations are added to waterway relations with the role tributary.
This causes problems in wikipedia, too as the WIWOSM system can not distinct between normal members and tributaries. While the Rhein is displayed nice in wikipedia/WIWOSM, the Seine looks pretty bad with all the tributaries.
--Werner2101 14:49, 28 December 2012 (UTC)
Yes, we need
We need some way to get together all members of a water basin, since it's one of the most important geographical features. This means also getting together the borders, i.e., the ridges, actually what is called a watershed, since actually it constitutes the shed, that is a sort of surface shape, not the waterways. The watershed is defineed by the topographic limits. Like in a multipolygon, the ridges constitutes the outer ways, in the shape of a closed multipolygon. Actually I would prefer to call this sort of relation as "water_basin" or "drainage_basin" (https://en.wikipedia.org/wiki/Drainage_basin). Also not as https://wiki.openstreetmap.org/wiki/Key:basin, since it's natural, not man made. I'd prefer something like natural=water_basin
basins, composed of divides
I would like to draw drainage divides, I don't particularly care of their graphic representation, but I do think it's a valuable piece of information. As Sergio above says, we would draw the drainage_divides/watersheds (type:way), and group them in drainage_basins (type:relation). I prefer the British English names, they assume less previous knowledge from non native speakers. we already have a waterway=drain, we can have a natural=drainage_divide for the borders, and natural=drainage_basin for the relation.
To make it possibly more concrete, consider this picture: the type:way natural=drainage_divide would be the red lines (Hauptwasserscheiden), while the type:relation natural=drainage_basin would be the greenish areas (Flusseinzugsgebiete). These relations would use a section of type:way natural=coastline to close the ring.