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NAME

v.dissolve - Dissolve boundaries between adjacent areas sharing a common category number

KEYWORDS

vector, area

SYNOPSIS

v.dissolve
v.dissolve help
v.dissolve input=name output=name [layer=integer] [--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
Default: 1

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. 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.

(GRASS Shell Script)

EXAMPLES

Basic use

v.dissolve input=undissolved output=dissolved

Dissolving based on column attributes

# check column names:
v.info -c polbnda_italy

# reclass based on desired column:
v.reclass polbnda_italy out=polbnda_italy_recl_nam col=vmap_nam

# dissolve:
v.dissove input=polbnda_italy_recl_nam output=pol_italy_regions

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

# reclass based on desired column:
v.reclass clc2000_clean out=clc2000_recl col=CODE_00

# dissolve:
v.dissolve input=clc2000_recl output=clc2000_final

SEE ALSO

v.category, v.centroids, v.extract, v.reclass

AUTHORS

module: M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand
help page: Trevor Wiens

Last changed: $Date: 2006/11/19 20:02:56 $


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