[GRASS-user] Re: grass-user Digest, Vol 50, Issue 55

[Richard Chirgwin]

>
> Message: 5
> Date: Tue, 22 Jun 2010 01:18:34 +0200
> From: stn <stneumann at web.de>
> Subject: [GRASS-user] Overlay vector map with points
> To: Martin Landa <landa.martin at gmail.com>
> Cc: grass list <grass-user at lists.osgeo.org>
> Message-ID:
> 	<AANLkTimdeuAo3MtmQSlhvoX7K98B63X6hsiR1j7tWF_o at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> Hi,
>
> I have a vector-map with polygons and a set of points imported with
> v.in.ascii, both in the same location and every point is in exactly one
> polygon.
>
> Both maps seem to be ok, their data can be queried.
>
> Now I would like to know which points lie in which polygon of the
> vector-map.
>
> For two vector-maps overlaying worked fine. But with the polygons and the
> points it does not seem to work. The maps can be overlayed but the
> statistics of the combined map show the attributes of the polygons and empty
> (though existing) columns for the attributes of the points.
>
> THX
> stn
Hi,

You don't need to overlay the points and polygons to answer this question.

Add a column to the points map to contain a polygon attribute. For eg:
v.db.addcol <point map> columns="Polygon_Cat int"

Then v.distance to work out which polygon the point is in:
v.distance from=<point map> from_type=point to=<polygon map> 
to_type=area dmax=0 upload=to_attr column=Polygon_Cat to_column=cat

Richard