[GRASS-user] Polygons and centroids

[Markus Neteler]

Dr. Manuel Seeger wrote on 10/31/2007 01:51 PM:
> Hallo all!
>
> I'm struggling with the import of a shapefile. It imports more  than 300
> of 1200 polygons without centroid.
>   

First of all, check (e.g. with ogrinfo) how many polygons you
really have.
It is rather likely that you have a topologically broken SHAPE
file - in this case lots of spurious polygons will be created (since
they are present like this in the map) unless you use
 - snap parameter (careful to not snap too much)
-  min_area can be used to suppress small areas

or later v.clean/v.edit with approriate parameters.

Unfortunately it is rather painful to fix broken SHAPE files.
At least you have a topological GIS at hand which helps you
to identify the problems. And yes, public, official SHAPE files
are also sometimes broken (I can indicate some if you want).

> Is there a way to select all these areas for getting them exclusively
> displayed?
E.g., v.digit should show broken topology in red.

Markus