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) $

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