v.dissolve(1grass) GRASS GIS User's Manual v.dissolve(1grass)
NAME
v.dissolve - Dissolves boundaries between adjacent areas sharing a
common category number or attribute.
KEYWORDS
vector, dissolve, area, line
SYNOPSIS
v.dissolve
v.dissolve --help
v.dissolve input=name [layer=string] [column=name] output=name
[--overwrite] [--help] [--verbose] [--quiet] [--ui]
Flags:
--overwrite
Allow output files to overwrite existing files
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog
Parameters:
input=name [required]
Name of input vector map
Or data source for direct OGR access
layer=string
Layer number or name.
Vector features can have category values in different layers. This
number determines which layer to use. When used with direct OGR ac-
cess this is the layer name.
Default: 1
column=name
Name of attribute column used to dissolve common boundaries
output=name [required]
Name for output vector map
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) re-
tains 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.re-
class 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 de-
tails.
Merging of areas can also be accomplished using v.extract -d which pro-
vides 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.list type=vector pat="clc2000_*" separator=","` 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
SOURCE CODE
Available at: v.dissolve source code (history)
Accessed: unknown
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GRASS 7.8.7 v.dissolve(1grass)
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