<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>GRASS GIS: v.dissolve</title> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link rel="stylesheet" href="grassdocs.css" type="text/css"> </head> <body bgcolor="white"> <img src="grass_logo.png" alt="GRASS logo"><hr align=center size=6 noshade> <h2>NAME</h2> <em><b>v.dissolve</b></em> - Dissolves boundaries between adjacent areas sharing a common category number or attribute. <h2>KEYWORDS</h2> vector, area, dissolve <h2>SYNOPSIS</h2> <b>v.dissolve</b><br> <b>v.dissolve help</b><br> <b>v.dissolve</b> <b>input</b>=<em>name</em> <b>output</b>=<em>name</em> [<b>layer</b>=<em>integer</em>] [<b>column</b>=<em>string</em>] [--<b>overwrite</b>] [--<b>verbose</b>] [--<b>quiet</b>] <h3>Flags:</h3> <DL> <DT><b>--overwrite</b></DT> <DD>Allow output files to overwrite existing files</DD> <DT><b>--verbose</b></DT> <DD>Verbose module output</DD> <DT><b>--quiet</b></DT> <DD>Quiet module output</DD> </DL> <h3>Parameters:</h3> <DL> <DT><b>input</b>=<em>name</em></DT> <DD>Name of input vector map</DD> <DT><b>output</b>=<em>name</em></DT> <DD>Name for output vector map</DD> <DT><b>layer</b>=<em>integer</em></DT> <DD>Layer number. If -1, all layers are extracted</DD> <DD>Default: <em>1</em></DD> <DT><b>column</b>=<em>string</em></DT> <DD>Name of column used to dissolve common boundaries</DD> </DL> <H2>DESCRIPTION</H2> The <EM>v.dissolve</EM> 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. Optionally, a column can be defined which is used to find adjacent polygons with identical attribute for common boundary dissolving. 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 <em>v.centroids</em>), 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 <em>v.category</em> for more details. <P> Merging of areas can also be accomplished using "<tt><em>v.extract</em> <b>-d</b></tt>" which provides some additional options. In fact, <EM>v.dissolve</EM> is simply a front-end to that module. The use of the <EM>column</EM> parameter adds a call to <EM>v.reclass</EM> before. <p> <EM>(GRASS Shell Script)</EM> <h2>EXAMPLES</h2> <h3>Basic use</h3> <div class="code"><pre> v.dissolve input=undissolved output=dissolved </pre></div> <br> <h3>Dissolving based on column attributes</h3> <div class="code"><pre> # check column names: v.info -c polbnda_italy # dissolve based on column attributes: v.dissolve input=polbnda_italy output=pol_italy_regions col=vmap_nam </pre></div> <br> <h3>Dissolving adjacent SHAPE files to remove tile boundaries</h3> 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: <div class="code"><pre> # 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 </pre></div> <H2>SEE ALSO</H2> <EM> <A HREF="v.category.html">v.category</A>, <A HREF="v.centroids.html">v.centroids</A>, <A HREF="v.extract.html">v.extract</A>, <a HREF="v.reclass.html">v.reclass</a> </EM> <H2>AUTHORS</H2> module: M. Hamish Bowman, Dept. Marine Science, Otago University, New Zealand<br> Markus Neteler for column support <BR> help page: Trevor Wiens <P> <i>Last changed: $Date: 2007-03-04 19:13:15 +0100 (Sun, 04 Mar 2007) $</i> <HR> <P><a href="index.html">Main index</a> - <a href="vector.html">vector index</a> - <a href="full_index.html">Full index</a></P> <P>© 2003-2008 <a href="http://grass.osgeo.org">GRASS Development Team</a></p> </body> </html>
