I was wondering if there is a good (or best practice) approach on how to merge geometry features that are touching or overlapping and have one common value in one table field.
Here is what I was trying to do: given a large dataset such as the (detailed NHD data layer) of rivers in California I created multiple buffers and inserted the results into a new table with one geometry column adding a score value to each of the same buffers distances used. Thus the buffer polygon layer has a score with a value of 10,100,500 and 1000 m corresponding to the buffer distance used. Given the approach I used to create the buffers those are often spatially overlapping (because there was no merge operation of the buffers and because the rivers are split along the flow line in multiple segments by node in the source shape file). The resulting layer works ok for my purposes (which is to retrieve information in which buffers a certain location is intersecting it with the river buffer (results can be 10,100,500 and 1000 or no intersect with the buffers). Now the layers is about 20 GB big disk size having a lot of unnecessary geometries with are overlapping. How can I go about merging all the existing geometries on this huge data set into a result layer that has (optimally ) only 4 polygons with the result scores to find my intersects. When I tried some of my own approaches (e.g. using st_collect and such to do this) so far whenever I started these sever resource intensive operations soon these where aborted by the system because i got some kind of out of memeonry errosr on my server (an ubuntu achjien). Is there a good way to optimize this kind of query operation without using 100% of my server ram so that I will not run out of memory or resulting in a lengthy query that would be running for 6 weeks or so :-) ? Any query examples or general insight are greatly appreciated . Cheers Karsten Karsten Vennemann Terra GIS Ltd 2119 Boyer Ave E Seattle, WA 98112 USA tel ++ 206 905 1711 fax ++ 925 905 1711
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