[OSM-dev] Applying outer way attributes to multi-polygons

Ben Supnik bsupnik at xsquawkbox.net
Mon Aug 2 19:13:33 BST 2010

Hi Y'all,

Does anyone have a good set of heuristics for the cases where 
OSM-reading software should treat outer-way attributes as applying to a 

 From what I can tell there are two possible cases I should look at:

- If the outer multipolygon has _no_ tags (other than type=multipolygon) 
then I should probably go get some attributes from the outer ways, or 
else the whole multipolygon is a no-op.

- If the outer multipolygon only has one way, then __maybe_- that way 
might contain all of the attributes I care about?  This second one makes 
me nervous because I could have a state park way where the boundary of 
the park is a water way with an island in it...the island (inner way) 
might be meant to cut a hole in some attributes (like water) but not 
others (like park).

I had some heuristics for my data processor I wrote about a year ago, 
but when re-running on newer planet data I found it was being fooled by 
the newer map, which has a lot more multipolygons and heavy reuse of ways.

If anyone is using a heuristic that has proven robust, I'd appreciate 
the hint! :-)

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