[GRASS-user] Query: number of 'areas' reported in v.build output does not necessarily represent different geographical areas

Nikos Alexandris nik at nikosalexandris.net
Fri May 10 11:40:37 PDT 2013

Markus M:

> > >> I assume the global mangroves map should not have overlapping
> > >> polygons, therefore as long as there are overlapping areas and/or the
> > >> number of centroids is not equal to the number of input polygons, more
> > >> cleaning is needed.

Nikos A:

> > > Unfortunately it seems there are overlapping polygons.

Markus M:

> > Obviously so, and fairly large overlapping areas according to your
> > output even for snap=1e-6: Overlapping area: 5.32085E+09 (41538 areas)

> > Therefore there are probably logical errors in the input data, for
> > example the same mangrove polygon might be present more than once.
> > This can not be cleaned automatically with v.in.ogr or v.clean. You
> > can investigate overlapping areas in the imported vector with d.vect
> > type=area layer=2 (only overlapping areas have a category in layer 2).

Nikos A:

> It looks _not_ good at all. Layer 2 over layer 1 uploaded at:
> <http://picpaste.com/global_mangroves_usgs_2011_imported_snap_1e-6_layer2_ov
> er_layer1-EWItDQK6.png>.

Sorry, more details:

# drawn in G7
d.vect global_mangroves_usgs_2011_06 layer=1 fcolor=red color=red
d.vect global_mangroves_usgs_2011_06 layer=2 fcolor=blue color=blue



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