[GRASS-user] topological errors in v.extract results

Blumentrath, Stefan Stefan.Blumentrath at nina.no
Wed Aug 17 00:19:01 PDT 2016

Dear all,

At the moment I am struggling quite a bit with GRASS topology errors for two of my maps which result from v.dissolve.

Input maps are imported with v.in.ogr without topological errors. However, the output maps from v.dissolve result into

406458 areas, but only
182176 centroids
in map A and

1058018 areas, but only
995283 centroids
in map B

After patching and cleaning both layers v.to.db gives no correct result for sides. Often areas have -sides like this:

Then I ran v.build -e on both in order to investigate.
For both, the number of errors reported by v.build is exactly the difference between the number of areas and the number of centroids in each map.

Any hints or suggestions for alternative approaches to dissolving areas with common attributes?
I am interested in the individual areas (= one category and one entry in the attribute table per area) anyway and will try v.extract directly, if that sounds reasonable?

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