I have a polygon layer that contains some polygons inside of polygons. I need to be able to identify the polygons inside of polygons and discard the polygons inside of the polygons. What is the most efficient way of doing that?
Most efficient way to find if a polygon falls with in the boundary of another polygon using postgis
1what's the point of the union if the polygons are contained within the bigger ones? Are there holes? Otherwise the inner ones could be simply deleted, right?– underdark ♦Mar 15, 2013 at 17:55
Good point, removing that...– CLJMar 15, 2013 at 19:56
If the polygons need to be completely within larger polygons you can use ST_Contains, if they simply need to be touching at some point you can use ST_Intersects.
If they're completely within your union is just going to return the outer boundary of the larger polygon. Do you need to doughnut out the smaller polygons from the larger ones?
I see what you are saying, I don't actually need to union them, just need to take the boundary of the containing polygon and discard the polygons inside it.– CLJMar 15, 2013 at 18:04