.TH v.what.vect 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBv.what.vect\fR\fR  \- Uploads vector values at positions of vector points to the table.
.SH KEYWORDS
vector, sampling, database, position, querying, attribute table
.SH SYNOPSIS
\fBv.what.vect\fR
.br
\fBv.what.vect \-\-help\fR
.br
\fBv.what.vect\fR \fBmap\fR=\fIname\fR  [\fBlayer\fR=\fIstring\fR]  \fBcolumn\fR=\fIname\fR \fBquery_map\fR=\fIname\fR  [\fBquery_layer\fR=\fIstring\fR]  \fBquery_column\fR=\fIname\fR  [\fBdmax\fR=\fIfloat\fR]   [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBmap\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of vector points map for which to edit attributes
.br
Or data source for direct OGR access
.IP "\fBlayer\fR=\fIstring\fR" 4m
.br
Layer number or name
.br
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
.br
Default: \fI1\fR
.IP "\fBcolumn\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of attribute column to be updated with the query result
.IP "\fBquery_map\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of vector map to be queried
.br
Or data source for direct OGR access
.IP "\fBquery_layer\fR=\fIstring\fR" 4m
.br
Layer number or name
.br
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
.br
Default: \fI1\fR
.IP "\fBquery_column\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of attribute column to be queried
.IP "\fBdmax\fR=\fIfloat\fR" 4m
.br
Maximum query distance in map units (meters for ll)
.br
Default: \fI0.0\fR
.SH DESCRIPTION
\fIv.what.vect\fR transfers attributes from the \fBquery_map\fR\(cqs
attribute table into the \fBmap\fR\(cqs attribute table. The module can
be used to transfer attributes from the table of a polygon map into the
attribute table of a point vector map, as well as the other way around,
i.e., from a point map into the attribute table of a polygon map (See
examples). The script is based on \fIv.distance\fR.
.SH NOTES
The upload \fBcolumn\fR into which the query results are stored must be
present in \fBmap\fR. Use \fIv.db.addcolumn\fR to add one if needed.
.PP
Use the \fBdmax\fR parameter to control the query distance tolerance, i.e.,
how far \fBmap\fR\(cqs points/centroids can be from the \fBquery_map\fR features.
For further options, use \fIv.distance\fR.
.PP
In case of a multipoint input \fBmap\fR 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 \fBquery_map\fR polygons.
.PP
When transferring attributes from a point map into a polygon map,
\fBdmax\fR has to be larger than zero, i.e., it will be determined by the
distance between query points and polygon centroids. Importantly, distance
is in meters for latitude\-longitude locations.
.PP
In case that one or both input vector maps are 3D, features need to
touch also in the 3rd dimension (z coordinate) in order to transfer
attributes.
.SH EXAMPLES
In this example, the \(cqhospitals\(cq 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 \(cqurbanarea\(cq polygon map are transferred to hospital points
locations in \(cqmyhospitals\(cq map:
.br
.nf
\fC
g.copy vect=hospitals,myhospitals
v.db.addcolumn myhospitals column=\(dqurb_name varchar(25)\(dq
v.what.vect myhospitals query_map=urbanarea column=urb_name query_column=NAME
# verification:
v.db.select myhospitals
\fR
.fi
.PP
In this example, city names, population data and others from
Geonames.org country files are
transferred to selected EU CORINE landuse/landcover classes
(\(dqContinuous urban fabric\(dq, 111, and \(dqDiscontinuous urban fabric\(dq, 112).
Note: The example is in UTM projection to which the input maps have been
projected beforehand.
.br
.nf
\fC
# extract populated places from geonames
v.extract geonames_IT where=\(dqfeaturecla=\(cqP\(cq\(dq output=geonames_IT_cities
# add new column
v.db.addcol corine_code111_112_cities column=\(dqgnameid double precision\(dq
# transfer geonameid (3000m maximal distance between points and centroids)
v.what.vect corine_code111_112_cities query_map=geonames_IT_cities column=gnameid \(rs
            query_column=geonameid dmax=3000
# now gnameid can be used for v.db.join to join further
# attributes from geonames.org
\fR
.fi
.SH SEE ALSO
\fI
v.db.addcolumn,
v.db.select,
v.distance,
v.rast.stats,
v.what.rast,
v.what.rast3,
v.vect.stats
\fR
.SH AUTHOR
Markus Neteler
.SH SOURCE CODE
.PP
Available at: v.what.vect source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual