[OSM-dev] multipolygons - dealing with topology errors

Ben Supnik bsupnik at xsquawkbox.net
Tue Jul 21 03:36:21 BST 2009

Hi Y'all,

Two things about multipolygons:

1. My software now detects topologically broken multipolygons, e.g. 
cases where I can't form rings out of the node list.  Is this useful, or 
is this information already generated by things like pgsql?

2. While looking at one test set of data, I found a lake where one 
island (modeled as a hole in the lake multipolygon) had not been "sealed".

Mapnik simply ignored the island, but osmarender had linked the start 
and end of the ways to form the island.

I have learned from experience that it isn't useful for me to ask 
"what's the spec"...OSM is its own spec, etc. etc.

So I'll just ask: any comments?  Is one interpretation considered better 
or worse than the other?

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