.TH v.dissolve 1grass "" "GRASS 6.4.4" "Grass User's Manual"
.SH NAME
\fI\fBv.dissolve\fR\fR  - Dissolves boundaries between adjacent areas sharing a common category number or attribute.
.SH KEYWORDS
vector, area, dissolve
.SH SYNOPSIS
\fBv.dissolve\fR
.br
\fBv.dissolve help\fR
.br
\fBv.dissolve input\fR=\fIname\fR \fBoutput\fR=\fIname\fR  [\fBlayer\fR=\fIinteger\fR]   [\fBcolumn\fR=\fIstring\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR] 
.SS Flags:
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.PP
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR" 4m
.br
Name of input vector map
.IP "\fBoutput\fR=\fIname\fR" 4m
.br
Name for output vector map
.IP "\fBlayer\fR=\fIinteger\fR" 4m
.br
Layer number. If -1, all layers are extracted.
.br
A single vector map can be connected to multiple database tables. This number determines which table to use.
.br
Default: \fI1\fR
.IP "\fBcolumn\fR=\fIstring\fR" 4m
.br
Name of column used to dissolve common boundaries
.PP
.SH DESCRIPTION
The \fIv.dissolve\fR module is used to merge adjacent areas in a vector
map which share the same category value. The resulting merged area(s) retains
this category value. Alternatively an integer or string column can be defined
which is used to find adjacent polygons with identical attribute for common
boundary dissolving. In this case the categories are not retained, only the
values of the new key column. See the \fIv.reclass\fR help page for details.
.SH NOTES
GRASS defines a vector area as composite entity consisting of a set of
closed boundaries and a centroid. The centroids must contain a
category number
(see \fIv.centroids\fR), this number is linked to area attributes and
database links.
.PP
Multiple attributes may be linked to a single vector entity through
numbered fields referred to as layers. Refer to \fIv.category\fR for
more details.
.PP
Merging of areas can also be accomplished using
v.extract \-d which provides some additional options.
In fact, \fIv.dissolve\fR is simply a
front-end to that module. The use of the \fIcolumn\fR parameter
adds a call to \fIv.reclass\fR before.
.SH EXAMPLES
.SS Basic use
\fC
.DS
.br
v.dissolve input=undissolved output=dissolved
.br
.DE
\fR
.SS Dissolving based on column attributes
North Carolina data set:
\fC
.DS
.br
g.copy vect=soils_general,mysoils_general
.br
v.dissolve mysoils_general output=mysoils_general_families column=GSL_NAME
.br
.DE
\fR
.SS Dissolving adjacent SHAPE files to remove tile boundaries
If tile boundaries of adjacent maps (e.g. CORINE Landcover SHAPE files)
have to be removed, an extra step is required to remove duplicated
boundaries:
\fC
.DS
.br
# patch tiles after import:
.br
v.patch \-e \(gag.mlist type=vect pat="clc2000_*" sep=","\(ga out=clc2000_patched
.br
.br
# remove duplicated tile boundaries:
.br
v.clean clc2000_patched out=clc2000_clean tool=snap,break,rmdupl thresh=.01
.br
.br
# dissolve based on column attributes:
.br
v.dissolve input=clc2000_clean output=clc2000_final col=CODE_00
.br
.DE
\fR
.SH SEE ALSO
\fI
v.category,
v.centroids,
v.extract,
v.reclass
\fR
.SH AUTHORS
module: M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
.br
Markus Neteler for column support
.br
help page: Trevor Wiens
.PP
\fILast changed: $Date: 2011-09-04 15:23:30 +0200 (Sun, 04 Sep 2011) $\fR
.PP
Full index
.PP
© 2003-2014 GRASS Development Team