[Tagging] Giant river multipolygons

Martin Koppenhoefer dieterdreist at gmail.com
Fri Feb 1 17:52:14 GMT 2013

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)

> 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.

There is the problem that they might have several names (with
different, potentially overlapping boundaries). How could we manage
this? (Often also a very small piece of forest has its own name, but
together with other forest parts they form a named forest, which
itself might be part of yet another bigger named area of forest).

IMHO one idea would be to have distinct tags for
* landuse  - (an area where trees are grown and cut) use of the land
* landcover - (an area covered with trees) physical description of the
vegetation (or possibly absence of vegetation)
* natural - geographical features (e.g. a named forest) abstract

The natural=wood / landuse=forest distinction is flawed and creates
useless (IMHO) debates how to distinguish them, and which level of
human intervention still justifies the predicate (in this reading of
the key) "natural". In practise some mappers prefer natural=wood where
other mappers would set landuse=forest (for the exact same situation).

> 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

> 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".

not sure if this applies here, "relations are not categories" implies
you don't have to group stuff into relations which is already grouped
by their attributes (or defined by a polygon, e.g. all pharmacies in
Austria), but in the case of a river you are actually creating a
distinct object (the river) which wouldn't be clear otherwise (because
you cannot simply add all adjacent riverbanks, they might belong to
affluent rivers)


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