[Tagging] tagging the multipolygon model (was landuse and military)

Martin Koppenhoefer dieterdreist at gmail.com
Thu Oct 15 13:52:19 BST 2009


2009/10/14 sly (sylvain letuffe) <liste at letuffe.org>:

> In the holes continuity, it as been proposed that an area representing
> something inside another area would still be part of a multipolygon relation
> but with it's own tags.

no, this is not the case. Multipolygon says: the inner part is NOT
part of the outer polygon. If it is part just don't put a
multipolygon-relation (standard-case).

> this sounds great, requesting the surface of the big area is strait forward,
> rendering become easy (no "which one is over which one"), such a puzzle makes
> it easy to find problems, etc.

no, this is a case to be solved continuously - usually if one polygon
is entirely inside another the smaller one should be rendered above:
this should be generally solved by the renderers. Also, it can be
better in some cases not to use a solid fill but just an outline that
is rendered above the fills.

> But, this becomes harder and harder for the mapper. A big forest containing
> thousands lakes ? a landuse=residential containing park, cimetary, etc. ?
> I fear not every one is gone a make the effort.
> And after all, is it at all needed ?

let the mappers decide.

> In the "area inside area case" (not the partially overlapping areas case)
> We can resonably imagine that if a mapper has added such an area inside
> another, then either :
> - they can be both (a military area and a forest)
> - they can't be both (a lake and a forest)

well, even in the case lake inside a forest I'm not sure, if the
forest stops where there is the lake. Probably you can consider the
lake also part of the forest (when it's small), or to give a different
example: elementary school inside a residential area. Usually those
would be considered to be part of the residential area.

> Maybe if we just define/explain/(do our best not to create same key
> incompatibility, juste like this boundary=military propose to replace the
> ambiguous landuse=military for some cases)
> Same for natural, then what we've left ?
amenity? Finally almost all tags can become areas.

> A lake inside a forest, is not a forest
sure?

> A cimetary inside a residential is not a residential
+1

cheers,
Martin




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