Is there a way to search for and identify empty multipolygons? I am thinking specifically of municipal boundaries that once existed in a known area, but someone came along and (mistakenly/maliciously) deleted all of the members, but there is still likely useful information in the multipolygon relation.

asked 20 Nov '13, 19:41

eric22's gravatar image

eric22
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edited 25 Nov '13, 11:47

Vincent%20de%20Phily's gravatar image

Vincent de P... ♦
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Maybe this page can help you, it's a list of relations existing in OSM without any member (the first link, a text file): http://www.h-renrew.de/h/osm/osmchecks/02_Relationstypen/empty_relations.html

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answered 21 Nov '13, 19:37

Alecs01's gravatar image

Alecs01
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Please have a look at http://overpass-turbo.eu/s/1zk

This find all relations of type multipolygon that have a value for "admin_level".

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answered 21 Nov '13, 07:51

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Roland Olbricht
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How long does that need to run? Seems to very long - did not get a result after ~ 30s waiting even for very very high zoom levels.

(21 Nov '13, 21:25) aseerel4c26 ♦

This script finds some relevant relations, but only a small fraction of the ones in Alecs01's link. I'm not sure why...

(21 Nov '13, 21:45) eric22
2

Zoom levels doesn't apply here, the map of Overpass Turbo is not used here. The runtime may be up to 15 minutes.

The request searches world-wide, but only for relations tagged as "type=multipolygon" and with any value for "admin_level", thus no other kinds of relations are found.

In general, the systematic way would be to download a planet file and search through that file for all empty relations regardless of their tagging, but that's considerably more effort. It is probably what the h-renew tool does.

By contrast, Overpass aims to to hunt down more specific elements, e.g. municipalities.

(22 Nov '13, 07:21) Roland Olbricht

Hmm, OK, I think you're right, the other relations were probably type=boundary.

(22 Nov '13, 08:26) eric22

@Roland Olbricht: oh(!), thank you! Sorry, I was assuming the usual bbox query. Yes, not included in your script. And, logically, not possible for a relation with no members (→ no gelocation).

(22 Nov '13, 19:18) aseerel4c26 ♦
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question asked: 20 Nov '13, 19:41

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last updated: 25 Nov '13, 11:47

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