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<h2>NAME</h2>
<em><b>v.overlay</b></em> - Overlays two vector maps.
<h2>KEYWORDS</h2>
vector, geometry
<h2>SYNOPSIS</h2>
<b>v.overlay</b><br>
<b>v.overlay help</b><br>
<b>v.overlay</b> [-<b>t</b>] <b>ainput</b>=<em>name</em> [<b>atype</b>=<em>string</em>[,<i>string</i>,...]] [<b>alayer</b>=<em>integer</em>] <b>binput</b>=<em>name</em> [<b>btype</b>=<em>string</em>[,<i>string</i>,...]] [<b>blayer</b>=<em>integer</em>] <b>output</b>=<em>name</em> [<b>operator</b>=<em>string</em>] [<b>olayer</b>=<em>integer</em>[,<i>integer</i>,...]] [--<b>overwrite</b>] [--<b>verbose</b>] [--<b>quiet</b>]
<h3>Flags:</h3>
<DL>
<DT><b>-t</b></DT>
<DD>Do not create attribute table</DD>
<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>ainput</b>=<em>name</em></DT>
<DD>Name of input vector map</DD>
<DT><b>atype</b>=<em>string[,<i>string</i>,...]</em></DT>
<DD>Type</DD>
<DD>Feature type(s)</DD>
<DD>Options: <em>line,area</em></DD>
<DD>Default: <em>area</em></DD>
<DT><b>alayer</b>=<em>integer</em></DT>
<DD>Layer number</DD>
<DD>A single vector map can be connected to multiple database tables. This number determines which table to use.</DD>
<DD>Default: <em>1</em></DD>
<DT><b>binput</b>=<em>name</em></DT>
<DD>Name of input vector map</DD>
<DT><b>btype</b>=<em>string[,<i>string</i>,...]</em></DT>
<DD>Type</DD>
<DD>Feature type(s)</DD>
<DD>Options: <em>area</em></DD>
<DD>Default: <em>area</em></DD>
<DT><b>blayer</b>=<em>integer</em></DT>
<DD>Layer number</DD>
<DD>A single vector map can be connected to multiple database tables. This number determines which table to use.</DD>
<DD>Default: <em>1</em></DD>
<DT><b>output</b>=<em>name</em></DT>
<DD>Name for output vector map</DD>
<DT><b>operator</b>=<em>string</em></DT>
<DD>Operator defines features written to output vector map</DD>
<DD>Feature is written to output if the result of operation 'ainput operator binput' is true. Input feature is considered to be true, if category of given layer is defined.</DD>
<DD>Options: <em>and,or,not,xor</em></DD>
<DD>Default: <em>or</em></DD>
<DD><b>and</b>: also known as 'intersection' in GIS</DD>
<DD><b>or</b>: also known as 'union' in GIS (only for atype=area)</DD>
<DD><b>not</b>: features from ainput not overlayed by features from binput</DD>
<DD><b>xor</b>: features from either ainput or binput but not those from ainput overlayed by binput (only for atype=area)</DD>
<DT><b>olayer</b>=<em>integer[,<i>integer</i>,...]</em></DT>
<DD>Output layer for new category, ainput and binput</DD>
<DD>If 0 or not given, the category is not written</DD>
<DD>Default: <em>1,0,0</em></DD>
</DL>
<h2>DESCRIPTION</h2>
<em>v.overlay</em> allows the user to overlay two vector area maps.
<!-- This is outdated
There are 3 links attached to features in output map,
<ul>
<li><b>field 1</b>: link to the new table, new table has 3 columns
<ul>
<li><b>cat</b> - key column linking rows to features
<li><b>cata</b> - category of <i>afield</i> from <i>ainput</i>
<li><b>catb</b> - category of <i>bfield</i> from <i>binput</i>
</ul>
<li><b>field 2</b>: category of <i>afield</i> from <i>ainput</i>
<li><b>field 3</b>: category of <i>bfield</i> from <i>binput</i>
</ul>
-->
The resulting output map has a merged attribute-table. The origin column-names
have a prefix (<em>a_</em> and <em>b_</em>) which results from the ainput- and binput-map.
<h2>NOTES</h2>
Currently only areas are supported for the operators <em>or</em> and <em>xor</em>! See also <a href="v.select.html">v.select</a>.
The operator defines what kind of operation will be done. Features are written to output,
if the result of an operation 'ainput operator binput' is true.
<p>
Attributes of the tables from ainput and binput are joined into a new table
linked to the output maps new cat-column.
<!-- This is outdated
<p>
<div class="code"><pre>
v.db.connect map=outputmap table=ainput.dbf field=2
v.db.connect map=outputmap table=binput.dbf field=3
</pre></div>
<p>
<b>Attention:</b> Removing the output map will also delete all tables linked to
it! Therefore it is advisable to copy tables from ainput and binput first and
connect the copied tables to the output map.-->
<h2>EXAMPLE</h2>
<div class="code"><pre>
v.overlay ainput=lake binput=province output=lakeXprovince
</pre></div>
<h2>SEE ALSO</h2>
<em>
<a href="v.db.connect.html">v.db.connect</a>,
<a href="v.select.html">v.select</a>,
<a href="g.copy.html">g.copy</a></em>
<h2>AUTHORS</h2>
Radim Blazek, ITC-Irst, Trento, Italy
<p><i>Last changed: $Date: 2007-10-25 17:54:40 +0200 (Thu, 25 Oct 2007) $</i>
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