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v.extract(1)		    GRASS GIS User's Manual		  v.extract(1)

NAME
       v.extract   -  Selects  vector features from an existing	vector map and
       creates a new vector map	containing only	the selected features.

KEYWORDS
       vector, extract,	select,	dissolve, random

SYNOPSIS
       v.extract
       v.extract --help
       v.extract	  [-dtr]	  input=name		[layer=string]
       [type=string[,string,...]]     [cats=range]    [where=sql_query]	  out-
       put=name	  [file=name]	  [random=integer]     [new=integer]	 [dis-
       solve_column=name]    [--overwrite]   [--help]	[--verbose]  [--quiet]
       [--ui]

   Flags:
       -d
	   Dissolve common boundaries (default is no)

       -t
	   Do not copy attributes (see also 'new' parameter)

       -r
	   Reverse selection

       --overwrite
	   Allow output	files to overwrite existing files

       --help
	   Print usage summary

       --verbose
	   Verbose module output

       --quiet
	   Quiet module	output

       --ui
	   Force launching GUI dialog

   Parameters:
       input=nameA [required]
	   Name	of input vector	map
	   Or data source for direct OGR access

       layer=string
	   Layer number	or name	('-1' for all layers)
	   A single vector map can be connected	to multiple  database  tables.
	   This	 number	 determines  which table to use. When used with	direct
	   OGR access this is the layer	name.
	   Default: 1

       type=string[,string,...]
	   Types to be extracted
	   Input feature type
	   Options: point, line, boundary, centroid, area, face
	   Default: point,line,boundary,centroid,area,face

       cats=range
	   Category values
	   Example: 1,3,7-9,13

       where=sql_query
	   WHERE conditions of SQL statement without 'where' keyword
	   Example: income < 1000 and population >= 10000

       output=nameA [required]
	   Name	for output vector map

       file=name
	   Input text file with	category numbers/number	ranges to be extracted
	   If '-' given	reads from standard input

       random=integer
	   Number of random categories matching	vector objects to extract
	   Number must be smaller than unique cat count	in layer

       new=integer
	   Desired new category	value (enter -1	to keep	original categories)
	   If new >= 0,	attributes is not copied
	   Default: -1

       dissolve_column=name
	   Name	of attribute column for	dissolving areas
	   Preserves category values

DESCRIPTION
       v.extract allows	a user to select vector	objects	from an	existing  vec-
       tor  map	 and  creates  a new map containing only the selected objects.
       Database	tables can be queried with SQL statements, if a	connection  is
       established.   Dissolving (optional) is based on	the output categories.
       If 2 adjacent areas have	the same output	category, the boundary is  re-
       moved.

       If  cats, file, random or where options are not specified, all features
       of given	type and layer are extracted. Categories are  not  changed  in
       that case.

NOTES
       Only  features with a category number in	the selected layer will	be ex-
       tracted.	So if you want to extract boundaries (which are	usually	 with-
       out  category,  as that information is normally held in the area's cen-
       troid) you must first use v.category to add them, or use	layer=-1.

EXAMPLES
       The examples are	intended for the North Carolina	sample dataset:

   Extract areas by category number with dissolving #1:
       v.extract -d cats=1,2,3,4 input=soils_wake output=soil_groupa type=area new=0

       produces	a new vector soil_groupa, containing those areas  from	vector
       soils  which  have category numbers 1 thru 4; any common	boundaries are
       dissolved, and all areas	in the new map will be assigned	category  num-
       ber 0.

   Extract areas by category number with dissolving #2:
       v.extract -d cats=1-4 input=soils_wake output=soil_groupa type=area new=-1

       produces	 a new vector map soil_groupa containing the areas from	vector
       soils which have	categories 1 thru 4. Any common	 boundaries  are  dis-
       solved,	all  areas  in the new map will	retain their original category
       numbers 1 thru 4, since new was set to -1.

   Extract all areas and assign	the same category to all:
       v.extract input=soils_wake output=soil_groupa type=area new=1

       produces	a new vector map soil_groupa containing	all areas from	soils.
       No  common  boundaries  are dissolved, all areas	of the new map will be
       assigned	category number	1.

   Extract vectors with	SQL:
       v.extract input=markveggy.shp output=markveggy.1	new=13 \
	 where="(VEGTYPE = 'Wi') or (VEGTYPE = 'PS') or	(PRIME_TYPE='Wi')"

       produces	a new vector map with category number 13 if the	SQL  statement
       is fulfilled.

   Extract vector features which have the given	field empty:
       v.extract input=lakes output=lakes_gaps where="FTYPE is NULL"

   Extract vector features which have the given	field not empty:
       v.extract input=lakes output=lakes_ftype	where="FTYPE not NULL"

   Reverse extracting (behaves like selective vector objects deleting):
       Remove meteorological stations from map which are located above 1000m:
       # check what to delete:
       v.db.select precip_30ynormals where="elev > 1000"
       # perform reverse selection
       v.extract -r input=precip_30ynormals output=precip_30ynormals_lowland \
	 where="elev > 1000"
       # verify
       v.db.select precip_30ynormals_lowland

   Dissolving based on column attributes:
       # check column names:
       v.info -c zipcodes_wake
       # reclass based on desired column:
       v.reclass input=zipcodes_wake output=zipcodes_wake_recl_nam column=ZIPNAME
       # verify:
       v.info -c zipcodes_wake_recl_nam
       v.db.select zipcodes_wake_recl_nam
       # dissolve:
       v.extract -d input=zipcodes_wake_recl_nam output=zipcodes_wake_regions

       This  produces  a new vector map	with common boundaries dissolved where
       the reclassed attributes	of adjacent (left/right) areas are identical.

   Extract 3 random areas from geology map
       v.extract input=geology output=random_geology type=area random=3
       This creates a new map with three  random  categories  matching	areas.
       Note that there may be more than	one feature with the same category.

SEE ALSO
	v.category, v.dissolve,	v.reclass, GRASS SQL interface

AUTHORS
       R.L. Glenn, USDA, SCS, NHQ-CGIS
       GRASS 6 port by Radim Blazek

SOURCE CODE
       Available at: v.extract source code (history)

       Main  index  | Vector index | Topics index | Keywords index | Graphical
       index | Full index

       A(C) 2003-2020 GRASS Development	Team, GRASS GIS	7.8.3 Reference	Manual

GRASS 7.8.3							  v.extract(1)

NAME | KEYWORDS | SYNOPSIS | DESCRIPTION | NOTES | EXAMPLES | SEE ALSO | AUTHORS | SOURCE CODE

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