[OSM-dev] Tagging of multipolygons with holes within holes
Martin Koppenhoefer
dieterdreist at gmail.com
Wed Oct 17 10:19:59 BST 2012
2012/10/17 Igor Brejc <igor.brejc at gmail.com>:
> 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.
+1, the paragraph about "inner outer-ways" always bugged me, because
it makes stuff more complicated. Actually you won't need to attach
this way: http://www.openstreetmap.org/browse/way/9245393 as outer to
this multipolygon http://www.openstreetmap.org/browse/relation/11104
(example from OP).
While valid according to the specs, it isn't the easiest (and most
transparent or stable) way to represent this situation, neither for
the mapper nor for the data consumer. You can remove this building
from the MP and still have the same semantics.
What IMHO should be done instead is to move the tags military =
barracks name = Stiftskaserne from the MP to the outer way, as they
apply to the whole area, and not only to the parts that are buildings.
Mixing tags from the outer ways and the relation to interpret what
kind of object the relation represents is odd. Things would be much
clearer if tags applying to the relation must go into the relation and
would never be inherited by outer ways. This would be obvious if we
had a "multipolygon-area kind of data type" like Jochen suggests.
cheers,
Martin
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