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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. |
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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". 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
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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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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 |
