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.
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 number 0.
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 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_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.
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=lakes output=lakes_gaps where="FTYPE is NULL"
v.extract input=lakes output=lakes_ftype where="FTYPE not NULL"
# 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
# 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.
v.extract input=geology output=random_geology type=area random=3
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