[Tagging] Giant river multipolygons

Masi Master masi-master at gmx.de
Fri Feb 1 23:01:56 GMT 2013

Am 01.02.2013, 18:52 Uhr, schrieb Martin Koppenhoefer  
<dieterdreist at gmail.com>:

> 2013/2/1 Masi Master <masi-master at gmx.de>:
>> 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=* +  
>> ...
> Yes, (currently it seems as if the "new" tagging cannot establish
> itself, according to taginfo not even 1% of all rivers mapped as areas
> use this scheme)

I think this is because there is no retagging the old style to the new.

>> 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.
> yes, this is also already done (at least with routes), but it creates
> new problems, because it might not be clear, which of the tags get
> inherited and which don't. Would you only set the name-tag to the
> superrelation containing smaller forests, or also the forest-tag? If
> you added also the forest tag: wouldn't that duplicate the forest? If
> you don't do it, how would you know which tags to inherit from the
> sub-relations?

A good example is the Lake Constance (de:Bodensee):
The whole Lake contains 3 parts: Untersee, Seerhein and Obersee
The first and last part contains another parts.

In my opinion, we can tag all sub-parts with natural=water and their  
names. Then, if we don't like to tag natural=water again, we need to put  
this multipolygon into another, to keep the connection to the object. So  
the whole lake is a construct of three parts, which contains the other  
sub-parts. And if the sub-parts (child-parts) all are natural=water, so  
the whole lake know, it is "water", too.

But, a multipolygon is created by the outer-line, not an area. So areas  
(like child multipolygons) are not allowed (without changing this piont of  

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