## NAME

v.category

## DESCRIPTION

v.category attaches, deletes or reports vector categories to map geometry. These categories (IDs) are used to link geometry object(s) to attribute records (from attribute table linked to vector map).

## NOTES

Use v.to.db to upload related categories to a linked attribute table.

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

to find out the geometry ids of certain features.

## EXAMPLES

### Report vector categories

    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

### Delete all vector categories in layer 1

    v.category input=testmap output=outmap option=del

### Add vector categories in layer 1 with step=2

    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

### Add categories/centroids to a vector map without categories

    v.category input=wkt output=wktnew option=add

Results can be tested using d.what.vect.

### Print vector categories of given layer

Print vector categories from the first layer, only for feature ids 1-50.

    v.category input=roads option=print layer=1 id=1-50

## SEE ALSO

v.centroids, v.db.connect, v.edit, v.to.db

## AUTHOR

Radim Blazek, ITC-irst, Trento, Italy
Modified (the id parameter) by Martin Landa, FBK-irst (formerly ITC-irst), Trento, Italy, 2008/02

Last changed: $Date: 2011-11-08 10:42:51 +0100 (Tue, 08 Nov 2011) $

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