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 edited 25 Nov '13, 11:47  Vincent de P... ♦ |
2 Answers:
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". answered 21 Nov '13, 07:51  Roland Olbricht |
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 answered 21 Nov '13, 19:37  Alecs01 |
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.
This script finds some relevant relations, but only a small fraction of the ones in Alecs01's link. I'm not sure why...
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.
Hmm, OK, I think you're right, the other relations were probably type=boundary.
@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).