[OSM-dev] Polygon inner/outer relation in osm file

Jochen Topf jochen at remote.org
Tue Aug 23 15:53:21 UTC 2016

On Di, Aug 23, 2016 at 03:58:02 +0200, Martin Koppenhoefer wrote:
> > Il giorno 23 ago 2016, alle ore 15:21, Frederik Ramm <frederik at remote.org> ha scritto:
> > 
> > they can have missing or wrong inner/outer tags
> > (usually considered valid)... the C++/Python library "osmium" is
> > probably the most advanced in building proper polygons, or check out
> > osm2pgsql, imposm, or ogr2ogr which also have code to deal with that.
> recently we stumbled upon problematic behavior of current multipoligon processing in osm-carto, as it drops tags on inner relation members if the outer members (or the relation?) has the same tags. I believe this kind of "fix" should not be performed, it leads to problems if this kind of mapping was done on purpose, e.g. because of some properties being different.
> Not applying "magic guesswork" also leads to more predictable behavior and ultimately to mappers fixing the representation in case it was wrong.

This has been a long-standing problem. Unfortunately there is a lot of
data in OSM that is still tagged this way, so it is not an option to
just not do this anymore. Too many multipolygons (about 17,000) would
break. This is not the only problem with current multipolygon tagging,
and I am working on a "campaign" to get these fixed.

There is more background and some stats here:

Jochen Topf  jochen at remote.org  http://www.jochentopf.com/  +49-351-31778688

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