[Tagging] Giant river multipolygons

Masi Master masi-master at gmx.de
Fri Feb 1 17:13:48 GMT 2013

Am 28.01.2013, 17:31 Uhr, schrieb Martin Vonwald (imagic)  
<imagic.osm at gmail.com>:

> Am 28.01.2013 um 17:26 schrieb Tobias Knerr <osm at tobias-knerr.de>:
>> I'd like to hear your opinions.
> My opinion is your opinion: if there is no good reason for gigantic  
> areas, don't use them.


IMO the riverbank is similar to "landuse, natural or landcover" but  
explicit for rivers. The wiki say the same:
Common tagging: type=multipolygon + waterway=riverbank + name=* + ...
New tagging: type=multipolygon + NATURAL=WATER + water=river + name=* + ...
Can we split a large lake (or forest) with the same name into several  
(Mulit-)Polygons? I think no, because they have all the same name(?), but  
it would be nice. One solution could be a super-relation, that collect the  
smaller (sub) relations.

8 month ago, I found some errors at the Elbe-riverbank relation (Elbe is a  
large river in north part of Germany and 1-2 easter countries). The  
relation was build over 90 % in this [1] example.
The leftover [2] needs, that the tags goes to the realtion, so the older  
90 % was twice tagged as waterway, at the own (multi-)polygon, and at the  
whole multipolygon.
I changed it to examlpe [1] and the multipolygon-relation goes to an  
collection-relation, which collect all polygons and outers from the  
riverbank. But this is not good, because "relations are not categorys". I  
don't delete this relation, because we can't get all riverbanks from a  
river by a command. Or do we tag the waterway-segments with the name-tag,  
too? Is the name-tag at the river-line "waterway=river" not enought?

[1] http://wiki.openstreetmap.org/wiki/File:Make_river.png
[2] http://wiki.openstreetmap.org/wiki/File:Possible-river-relationship.png

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