v.category.1grass - Man Page

Attaches, deletes or reports vector categories to/from/of map geometry.


vector, category, layer


v.category --help
v.category [-gt] input=name  [layer=string[,string,...]]   [type=string[,string,...]]   [ids=range]   [output=name]  option=string  [cat=integer]   [step=integer]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]



Shell script style, currently only for report
Format: layer type count min max


Do not copy attribute table(s)


Allow output files to overwrite existing files


Print usage summary


Verbose module output


Quiet module output


Force launching GUI dialog


input=name [required]

Name of input vector map
Or data source for direct OGR access


Layer number or name
Vector features can have category values in different layers. This number determines which layer to use. When used with direct OGR access this is the layer name.
Default: 1


Input feature type
Options: point, line, boundary, centroid, area, face, kernel
Default: point,line,centroid,face


Feature ids (by default all features are processed)
Example: 1,3,7-9,13


Name for output vector map

option=string [required]

Action to be done
Options: add, del, chlayer, sum, report, print, layers, transfer
add: add a category to features without category in the given layer
del: delete category (cat=-1 to delete all categories of given layer)
chlayer: change layer number (e.g. layer=3,1 changes layer 3 to layer 1)
sum: add the value specified by cat option to the current category value
report: print report (statistics), in shell style: layer type count min max
print: print category values, layers are separated by ’|’, more cats in the same layer are separated by ’/’
layers: print only layer numbers
transfer: copy values from one layer to another (e.g. layer=1,2,3 copies values from layer 1 to layer 2 and 3)


Category value
Default: 1


Category increment
Default: 1


v.category attaches, copies, deletes or reports categories to/from/of vector geometry objects. Further on, v.category adds a number given by the cat option to categories of the selected layer. These categories (IDs) are used to assign IDs or to group geometry objects into categories (several different geometry objects share the same category). These categories are also used to link geometry object(s) to attribute records (from an attribute table linked to vector map).


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 wxGUI vector digitizer or by running v.category with the type parameter set to area.

If categories are copied with option=transfer, a warning is issued if categories already exit in the layer they are copied to. In this case the user must make sure beforehand that copying categories from one layer to another layer does not cause undesired grouping of different geometry objects into the same categories. This can be avoided by specifying only one layer. The module will then find the next free layer number and copy categories to there. The new layer number is reported at the end.

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 for type=area.

The cat parameter is only used with option=add, option=sum and option=del.

Categories can be deleted for the given layer with option=del. If cat is set to -1, all categories for the given layer are deleted. If cat is zero or positive, only this category value will be deleted. By default, cat is set to 1 which means that only categories of value 1 will be deleted.

With option=report, the module reports for each layer and type the total number of categories, the minimum and the maximum category number. If there are e.g. two lines with line 1 having category 1 and line 1 having categories 1 and 2, then there are a total of three category values with minimum 1 and maximum 2.

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.


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 cat=-1

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.

Copy categories from layer 1 to layer 2,3,4,5,6,7 and 8

Existing layer will be overwritten, non-existing will be created.

v.category input=observer output=observer_new option=transfer layer=1,2,3,4,5,6,7,8

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


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

Source Code

Available at: v.category source code (history)

Accessed: Tuesday Mar 19 11:02:17 2024

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