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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 06:23:30 -0700 (Sun, 04 Sep 2011) $

       Full index

       © 2003-2013 GRASS Development Team



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