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

Markus Metz markus.metz.giswork at gmail.com
Thu May 9 05:23:35 PDT 2013

On Thu, May 9, 2013 at 6:51 AM, RichardC <richtcooper at hotmail.com> wrote:
>> Does using smaller values improve topology?

Smaller values for the snapping threshold cause less modifications.
The idea is to modify the original data as little as possible and as
much as necessary. Thus...

> The approach I'd take would be to gradually reduce the snapping distanceby a
> factor of 10  (e.g., starting at 0.000001) until no changes in topology are
> apparent.

... I would start with a very low threshold and gradually increase the
threshold by a factor of 10 until no more errors occur.

Then I'd address the minimum size area to be imported to see how
> that affects topology.

That might have no effect because the minimum size applies to original
polygons, not to small overlapping areas.

> Unless there is an easier/quicker way?
> Richard
> GRASS 6.4.3

Faster with GRASS 7, otherwise not really, unless you know exactly how
the dataset to be imported was created (the equivalent of v.info -h).

Markus M

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