The type parameter specifies the type of geometry objects to which the category is added; it is similar to an input filter - only the geometry specified in 'type' is processed.
If the type parameter is set to centroid and the option parameter set to add, new categories will be added to existing centroids. Note however, that new centroids cannot be created this way. To do so, they must be added manually using v.digit or by running v.category with the type parameter set to area.
Areas are a special case because it is impossible to attach a cat to an area without a centroid; in this case, the module places new centroids in areas automatically.
The cat parameter is only used with option=add and option=sum.
The ids parameter specifies the list of feature IDs to which the operation is performed; by default, all vector feature ids are processed. The feature ID is an internal (unique) geometry ID that all vector primitives possess, and is separate from any category the feature may also possess. Use
v.edit map=inputname tool=select
v.category input=testmap option=report LAYER/TABLE 1/testmap: type count min max point 0 0 0 line 1379 1 1379 boundary 0 0 0 centroid 0 0 0 area 0 0 0 all 1379 1 1379
v.category input=testmap output=outmap option=del
v.category input=outmap output=stepmap option=add step=2 # report v.category input=stepmap option=report LAYER/TABLE 1/outmap: type count min max point 0 0 0 line 1379 1 2757 boundary 0 0 0 centroid 0 0 0 area 0 0 0 all 1379 1 2757
v.category input=wkt output=wktnew option=add
v.category input=roads option=print layer=1 id=1-50
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