v.extract -d list=1,2,3,4 input=soils output=soil_groupa type=area new=1
produces a new vector area file soil_groupa containing 'area' boundaries from soils with area category numbers of 1 thru 4; any common boundaries are dissolved, and all areas of the new map will be assigned category number 1.
v.extract -d list=Abc,Def1,12A,WWd input=soils output=soil_groupa type=area new=0
produces a new vector area file soil_groupa containing 'area' boundaries from soils with area category labels of Abc,Def1, 12A,WWd; these labels correspond to numbers 1 thru 4 of soils. Any common boundaries are dissolved, all areas of the new map will be retain their original category numbers 1 thru 4, in this case, since new was set to 0.
v.extract input=soils output=soil_groupa type=area new=1 file=sample
produces a new vector area file soil_groupa containing 'area' boundaries 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=1 \ where="(VEGTYPE = 'Wi') or (VEGTYPE = 'PS') or (PRIME_TYPE='Wi')"
produces a new vector map with category label 1 if the SQL statement is fulfilled.
# 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
This produces a new vector map with common boundaries dissolved where the reclassed attributes of adjacent (left/right) polygons 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
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