GRASS 6 Terminology

• LOCATION: This is the name of an available geographic location.

• MAPSET: Every GRASS session runs under the name of a MAPSET. A MAPSET may be a geographical subset or as large as the parent LOCATION. Technically they are subdirectories under any location. In a networked environment with several users working within the same location, mapsets play a special role. Users may only select (and thus modify) a mapset that they own (i.e., have created). However, data in all mapsets for a given location can be read by anyone (unless prevented by UNIX file permissions). The "PERMANENT" mapset usually contains the read-only base maps like the elevation model, while the other locations are readable and writable by their owners. The "PERMANENT" mapset also contains some information about the location itself that is not found in the mapsets (projection info etc.), thus it must exist in every location.

• DATABASE: This is the unix directory containing the geographic LOCATIONS (also called GISDBASE)

• REGION: The REGION may be the entire area or subset of the chosen LOCATION.

• WINDOW: see REGION

Sample GRASS 5.0 database directory tree structure (Spearfish data set)

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• CELL DATA TYPE: a raster map from INTEGER type (whole numbers only)

• FCELL DATA TYPE: a raster map from FLOAT type (4 bytes, 6 digits precision)

• DCELL DATA TYPE: a raster map from DOUBLE type (8 bytes, 10 digits precision)

• NULL: represents "no data" in raster maps, to be distinguished from 0 (zero) data value

• INTEGER MAP: see CELL DATA TYPE

• FLOAT MAP: see FCELL DATA TYPE

• DOUBLE MAP: see DCELL DATA TYPE

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• CATEGORY NUMBER: A numerical value for a map feature (e.g. road number). Also sometimes called CATEGORY VALUE.

The CATEGORY NUMBER is related to the attribute database. The internal vector feature ID is different from this.

8 LAYER: A single vector map can be connected to multiple database tables. This number determines which table to use.

see the GRASS 7 Terminology page for more discussion.