Geografic-Information-System/scripts/v.what.vect/v.what.vect.html

<h2>DESCRIPTION</h2>

<em>v.what.vect</em> transfers attributes from the <b>qvector</b>'s map
attribute table into the attribute table of <u>points</u> present in the
<b>vector</b> map. The script is based on <em>v.distance</em>.

<h2>NOTES</h2>

The upload <b>column</b>, into which the query results are stored, must be
present in the <b>vector</b> map. Use <em>v.db.addcolumn</em> to add one if needed.
<p>Use dmax parameter to control query distance tolerance (how far points/centroids
can be from <b>qvector</b> features). For more options, use
<em>v.distance</em> instead.
<p>In case of a multipoint input <b>vector</b> map, with several points having the
same category number, it can happen, that the query result is NULL, if the same
category number falls into different <b>qvector</b> polygons.
<p>When transferring attributes from a point map to a polygon map, usually <b>dmax</b>
has to be larger than zero (determined by distance between query points and
polygon centroids).

<h2>EXAMPLES</h2>

In this example, the 'hospitals' point map in the North Carolina location is
copied to the current mapset, a new attribute column is added and the urban
names from the 'urbanarea' polygon map are transferred to the 'myhospitals'
map at the hospital points' locations:

<div class="code"><pre>
g.copy vect=hospitals,myhospitals
v.db.addcolumn myhospitals column="urb_name varchar(25)"
v.what.vect myhospitals qmap=urbanarea column=urb_name qcolumn=NAME
# verification:
v.db.select myhospitals
</pre></div>
<p>
In this example, city names, population data and more from
<a href="http://download.geonames.org/export/dump/">Geonames.org country files</a> are
transferred to selected EU CORINE landuse/landcover classes
("Continuous urban fabric", 111, and "Discontinuous urban fabric", 112).
Note: Example in UTM projection to which the input maps have been projected
beforehand to have metric distances support:

<div class="code"><pre>
# extract populated places from geonames
v.extract geonames_IT where="featurecla='P'" output=geonames_IT_cities
# add new column 
v.db.addcol corine_code111_112_cities column="gnameid double precision"
# transfer geonameid (3000m maximal distance between points and centroids)
v.what.vect corine_code111_112_cities qmap=geonames_IT_cities column=gnameid \
            qcolumn=geonameid dmax=3000
# now gnameid can be used for v.db.join to join further
# attributes in from geonames.org
</pre></div>

<h2>SEE ALSO</h2>

<em>
<a href="v.db.addcolumn.html">v.db.addcolumn</a>,
<a href="v.db.select.html">v.db.select</a>,
<a href="v.distance.html">v.distance</a>,
<a href="v.rast.stats.html">v.rast.stats</a>,
<a href="v.what.rast.html">v.what.rast</a>
</em>


<h2>AUTHOR</h2>

Markus Neteler

<p><i>Last changed: $Date$</i>