[GRASS-user] Definition of Category for Vectors

GRASS GRASS user
1

Hi guys

I’ve been reading Neteler/Mitasova book and I have a question:
Regarding vector data, what is a category? and Why do I need to have category readers/writters? Because, for What I understood, a category is like a Feature ID that links a geometry to its attributes in a DB. Is this correct?

Thanks and thanks to Luis Lisboa for lending me the GRASS book (for 2 weeks :slight_smile: )

Best regards,
Pedro Roma

2

Pedro Roma wrote:

Hi guys

I've been reading Neteler/Mitasova book and I have a question:
Regarding vector data, what is a category?

A category specifies the category a vector feature belongs to, e.g. highway, major road, minor road for lines or land cover type for areas.

See also
http://grass.osgeo.org/grass64/manuals/html64_user/vectorintro.html

and Why do I need to have category readers/writters?

In order to change categories of features.

Because, for What I understood, a category is like a Feature ID that links a geometry to its attributes in a DB. Is this correct?

Yes. Also note that one feature can have several categories and several features can share the same category. A link to attributes in a DB is optional. An example for classified (categorized) vector features without a db link is given in
http://grass.osgeo.org/grass64/manuals/html64_user/v.lidar.edgedetection.html

Markus M