[postgis-users] Topology Issue Reported by Query but Not Identified with ST_IsValid

Regina Obe lr at pcorp.us
Thu May 26 21:47:55 PDT 2016

Try replacing your ST_Collect call with ST_Union.


ST_Collect when used with polygons will create invalid multipolygons since it just collects them up, and if they are adjacent, it's not a valid multipolygon.


Hope that helps,







From: postgis-users [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Michael Treglia
Sent: Thursday, May 26, 2016 10:34 PM
To: PostGIS Users Discussion <postgis-users at lists.osgeo.org>
Subject: [postgis-users] Topology Issue Reported by Query but Not Identified with ST_IsValid


Hi All,


I was running a query involving ST_Difference between two multipolygon layers, and a while in, it threw this message: 

ERROR: GEOSDifference: TopologyException: side location conflict at 919670.1768945494 140665.82566365649


However, I previously ran ST_MakeValid, and ST_IsValid doesn't report any objects with problems. Is there something I'm missing, or something else I need to check? (Apologies is this is just a naive question - still learning my way around PostGIS).


And in case it helps, here's my SQL:



SELECT gid, COALESCE(ST_Difference(geom_2263, (SELECT ST_Collect(b.geom_2263) 

                                         FROM citywide_basedata.parcels15 b

                                         WHERE ST_Intersects(a.geom_2263, b.geom_2263)

                                         )), a.geom_2263)

FROM citywide_basedata.boroughs_nowater a where boroname like 'Staten Island';




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