[OSM-talk] Multipolygon relations and disjunct geometries

Jochen Topf jochen at remote.org
Thu Sep 28 13:16:54 UTC 2017

On Thu, Sep 28, 2017 at 02:52:29PM +0200, Martin Koppenhoefer wrote:
> Recently I was presented with an Error message of my favorite editing
> software, when I tried to upload a changeset where several pyramids in Giza
> (Egypt) together are known by a common name.
> JOSM told me there was an Error in my data. An Error for the JOSM validator
> is something that is most likely wrong and should usually be fixed.
> The reason for the error was that I had created a multipolygon, but had
> left tags which are referring to an area, on the member objects (outer
> ways). This is something I believe is completely regular and happens as
> soon as some property of one of the members is not valid for the relation
> as a whole, e.g. because the name is different, etc.
> What is your opinion on this?

If the outer ring is a single closed way it is a polygon in its own
right and it is perfectly okay that it has its own (polygon) tags. Those
tags only apply to this particular way then.

If the outer ring is made up of several ways, the tags on them only apply
to each way by itself. If those are "line" tags, like highway, or
something like a wall, that is fine. But they can't be "polygon" tags
like landuse etc. because there is no polygon there. If you need this,
you'll need another multipolygon relation combining those ways.

This is somewhat different than the older interpretation when we still
had old-style multipolygons. But with the new-style multipolygons
interpretation, the tags from a collections of objects are *never*
aggregated into a larger whole.

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

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