[OSM-dev] Tagging of multipolygons with holes within holes

[Igor Brejc]

On Wed, Oct 17, 2012 at 9:40 AM, Frederik Ramm <frederik at remote.org> wrote:

>
> The area of the "hole within the hole" does not require special tagging,
> as it is covered by the multipolygon itself. If you have a forest with a
> hole in a hole, then that hole in a hole is forest as well.
>

True, but you need to determine that geometrically (see my previous answer)
and then apply the tagging rules down the "holes hierarchy".


>
> If you are, on the other hand, thinking of a "lake in the middle of a
> meadow in the middle of a forest" situation, then this is not "hole in a
> hole" - the forest has one hole which is the meadow, and the meadow has one
> hole which is the lake. You would have three ways:
>
> F - tagged as forest
> M - tagged as meadow
> L - tagged as lake
>
> and two multipolygons
>
> MP1: outer=F, inner=M
> MP2: outer=M, inner=L
>

Yes, if you split it in two separate multipolygons, then it's clear. But
the problem is that Wiki does not explicitly forbids (just recommends not
to) doing it all in a single multipolygon, quote:

Such cascading is still recommended when the "island" in the middle is
> something else than the area on the outside, but where the "island" is the
> same stuff it can just be made a hole in the hole.


Igor
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