

category - In GRASS, data are categorized by their distinguishing
characteristics (a.k.a., attributes or categories), such as depth to
water table, soil moisture, etc.  In a map layer, each unique attribute
type is tagged with a unique integer value called a \category value\
and a \category label\ describing the category contents; each map can
contain category values falling in the range +/- 2 to the 31.
Attribute values may be assigned to points (a.k.a., sites),
linear features, and area features.

