[OSM-talk] Using multipolygons as boundaries
frederik at remote.org
Sun Jan 4 21:08:36 GMT 2009
those of us who use relations to tag administrative boundaries
usually apply the schema described in
which suggests to use a type=boundary relation with "enclaves" and
"exclaves". At the time of conception, that was ok because
administrative areas (e.g. countries) often required border lines taht
consisted of many ways and exclaves, something that plain multipolygons
did not support.
Since we now have "advanced multipolygons" as described here:
(which, being true to their name, support any number of disjunct areas
which may have zero or more holes each, and even islands in holes and so
on), there is an equivalence between the two: each administrative area
corresponds to exactly one multipolygon.
I am thus suggesting that we drop using the special "type=boundary"
relation and instead use a simple "type=multipolygon" for administrative
areas. Everything else would stay the same (boundary=administrative,
admin_level=x, name=y, ...). Members would not carry the roles "exclave"
and "enclave" (which seem to have been difficult to understand for
some), but instead simply "outer" and "inner" just like with plain
I have described the suggested change in detail here:
The main advantage of this is that any piece of software that works with
our data would just have to understand multipolygons - wheter they are
additionally tagged as representing a boundary, a forest, a lake or
whatever - instead of having to carry a list of relation types that form
one or the other kind of area.
Frederik Ramm ## eMail frederik at remote.org ## N49°00'09" E008°23'33"
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