If list, file, random or where options are not specified, all features of given type and layer are extracted. Categories are not changed in that case.
v.extract -d list=1,2,3,4 input=soils 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 number 0.
v.extract -d list=1-4 input=soils 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 dissolved, all areas in the new map will retain their original category numbers 1 thru 4, since new was set to -1.
v.extract input=soils 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.
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.
v.extract input=forest output=forest_gaps where="CANOPY is NULL"
v.extract input=forest output=forest_canopy where="CANOPY not NULL"
# check what to delete: v.db.select gsod_stationlist where="latitude < -91" # perform reverse selection v.extract -r gsod_stationlist out=gsod_stationlist_clean where="latitude < -91" v.db.select gsod_stationlist_clean
# check column names: v.info -c polbnda_italy # reclass based on desired column: v.reclass polbnda_italy out=polbnda_italy_recl_nam col=vmap_nam # verify: v.info -c polbnda_italy_recl_nam v.db.select polbnda_italy_recl_nam # dissolve: v.extract -d polbnda_italy_recl_nam out=pol_italy_regions
produces a new vector map with common boundaries dissolved where the reclassed attributes of adjacent (left/right) areas are identical.
v.extract in=map_with_islands out=maps_without_islands list=1-99999 # and/or v.extract -d in=map_with_islands out=maps_without_islands
v.extract input=geology output=random_geology type=area random=3
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