[OSM-talk] Fixing broken multipolygons

Jochen Topf jochen at remote.org
Sat Mar 4 15:46:56 UTC 2017

On Sat, Mar 04, 2017 at 10:50:41AM +0100, Martin Koppenhoefer wrote:
> > On 4 Mar 2017, at 08:49, Jochen Topf <jochen at remote.org> wrote:
> > 
> > Looking at the graphs on http://area.jochentopf.com/stats you can see
> > that the number of (multi)polygons is growing steadily, while the number
> > of errors has been more or less flat over the last half year.
> nice stats and good results.
> I want to point out though that "
> Errors: Inner rings with same tags as outer rings"
> are not necessarily errors, and should not be "fixed" unless you know
> very well the situation and can tell that there's indeed a
> redundancy/data problem. E.g. you can have a building or building:part
> inside another building or building:part. These could be tagged still
> "incompletely" hence having just the same tags for the moment but be
> different objects nonetheless. Similarly woods inside woods, etc.

"Inner rings with same tags as outer rings" is a subset of old-style
multipolygons. Well, as you correctly point out, some of them might be
okay, but most of them are especially "bad" cases of old-style
multipolygons. And they are another good reason why we need to get rid
of old-style multipolygons. There is just no way to figure out
automatically, what's right here and what's not. So humans have to fix
those. I'll create Maproulette challenges for these too at some point.

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

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