GRASS GIS manual: v.overlay

NAME

v.overlay - Overlays two vector maps.

KEYWORDS

vector, geometry

SYNOPSIS

v.overlay
v.overlay help
v.overlay [-t] ainput=name [atype=string[,string,...]] [alayer=integer] binput=name [btype=string[,string,...]] [blayer=integer] output=name [operator=string] [olayer=integer[,integer,...]] [--overwrite] [--verbose] [--quiet]

Flags:

-t: Do not create attribute table
--overwrite: Allow output files to overwrite existing files
--verbose: Verbose module output
--quiet: Quiet module output

Parameters:

ainput=name: Name of input vector map (A)
atype=string[,string,...]: Feature type (vector map A); Feature type; Options: line,area; Default: area
alayer=integer: Layer number (vector map A); A single vector map can be connected to multiple database tables. This number determines which table to use.; Default: 1
binput=name: Name of input vector map (B)
btype=string[,string,...]: Feature type (vector map B); Feature type; Options: area; Default: area
blayer=integer: Layer number (vector map B); A single vector map can be connected to multiple database tables. This number determines which table to use.; Default: 1
output=name: Name for output vector map
operator=string: Operator defines features written to output vector map; 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.; Options: and,or,not,xor; Default: or; and: also known as 'intersection' in GIS; or: also known as 'union' in GIS (only for atype=area); not: features from ainput not overlayed by features from binput; xor: features from either ainput or binput but not those from ainput overlayed by binput (only for atype=area)
olayer=integer[,integer,...]: Output layer for new category, ainput and binput; If 0 or not given, the category is not written; Default: 1,0,0

DESCRIPTION

v.overlay allows the user to overlay two vector area maps. The resulting output map has a merged attribute-table. The origin column-names have a prefix (a_ and b_) which results from the ainput- and binput-map.

NOTES

Currently only areas are supported for the operators or and xor! See also v.select. 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.

Attributes of the tables from ainput and binput are joined into a new table linked to the output maps new cat-column.

EXAMPLE POLYGON TO POLYGON UNION

v.overlay ainput=lake binput=province output=lakeXprovince operator=or

EXAMPLE LINE TO POLYGON CLIPPING

Using the North Carolina sample dataset, we clip the roads map to the area of city of Raleigh:

g.region vect=zipcodes_wake

# extract Raleigh city
v.extract in=zipcodes_wake out=raleigh \
            where="ZIPNAME = 'RALEIGH'"

# clip road network to city polygon:
v.overlay ainput=roadsmajor atype=line binput=raleigh \
            out=roadsmajor_raleigh operator=and

v.overlay: Line to polygon clipping

AUTHORS

Radim Blazek, ITC-Irst, Trento, Italy

Last changed: $Date: 2011-02-09 06:57:16 -0800 (Wed, 09 Feb 2011) $

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