v.dissolve - Dissolves boundaries between adjacent areas sharing a common category number or attribute.
vector, area, dissolve
v.dissolve input=name output=name [layer=integer] [column=string] [--overwrite] [--verbose] [--quiet]
- Allow output files to overwrite existing files
- Verbose module output
- Quiet module output
- Name of input vector map
- Name for output vector map
- 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
- Name of column used to dissolve common boundaries
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.
GRASS defines a vector area as composite entity consisting of a set of
closed boundaries and a centroid. The centroids must contain a
(see v.centroids), this number is linked to area attributes and
Multiple attributes may be linked to a single vector entity through
numbered fields referred to as layers. Refer to v.category for
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.
v.dissolve input=undissolved output=dissolved
Dissolving based on column attributes
North Carolina data set:
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
# 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
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 06:23:30 -0700 (Sun, 04 Sep 2011) $
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