NAME¶
v.dissolve - Dissolves boundaries between adjacent areas sharing a
common category number or attribute.
KEYWORDS¶
vector, area, dissolve
SYNOPSIS¶
v.dissolve
v.dissolve help
v.dissolve input=
name output=
name
[
layer=
integer] [
column=
string]
[--
overwrite] [--
verbose] [--
quiet]
Flags:¶
- --overwrite
-
Allow output files to overwrite existing files
- --verbose
-
Verbose module output
- --quiet
-
Quiet module output
Parameters:¶
- input=name
-
Name of input vector map
- output=name
-
Name for output vector map
- layer=integer
-
Layer number. If -1, all layers are extracted.
A single vector map can be connected to multiple database tables. This
number determines which table to use.
Default: 1
- column=string
-
Name of column used to dissolve common boundaries
DESCRIPTION¶
The
v.dissolve 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
v.reclass help page for details.
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
v.centroids), this number is linked to area attributes and database
links.
Multiple attributes may be linked to a single vector entity through numbered
fields referred to as layers. Refer to
v.category for more details.
Merging of areas can also be accomplished using v.extract -d which provides some
additional options. In fact,
v.dissolve is simply a front-end to that
module. The use of the
column parameter adds a call to
v.reclass
before.
EXAMPLES¶
Basic use¶
v.dissolve input=undissolved output=dissolved
Dissolving based on column attributes¶
North Carolina data set:
g.copy vect=soils_general,mysoils_general
v.dissolve mysoils_general output=mysoils_general_families column=GSL_NAME
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:
# patch tiles after import:
v.patch -e `g.mlist type=vect pat="clc2000_*" sep=","`
out=clc2000_patched
# remove duplicated tile boundaries:
v.clean clc2000_patched out=clc2000_clean tool=snap,break,rmdupl thresh=.01
# dissolve based on column attributes:
v.dissolve input=clc2000_clean output=clc2000_final col=CODE_00
SEE ALSO¶
v.category, v.centroids, v.extract,
v.reclass
AUTHORS¶
module: M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
Markus Neteler for column support
help page: Trevor Wiens
Last changed: $Date: 2011-09-04 15:23:30 +0200 (Sun, 04 Sep 2011) $
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