Thanks for the responses. Have changed the original query from this: SELECT ST_ConvexHull(ST_Collect(ST_Force_2D(geom))) FROM table001 to this: SELECT ST_ConvexHull(ST_MemUnion(geom)) FROM table001 and its still running; over 12 hours now.Is this a waste of time.I'm trying it this way as I guessed it could be an aggregate approach issue after reading this post from Paul: http://blog.cleverelephant.ca/2009/01/must-faster-unions-in-postgis-14.html and was wondering if the union operation might work for my current requirements so set it running yesterday. The ST_Union gives the same array size error after a few seconds but as I said the ST_MemUnion is still running, but is it working or going to work!!! Anyway, thanks again for your feedback. Paul
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