Region settings

Revision as of 16:31, 24 November 2010

g.region is a very important module because it manages the boundary definitions for geodata. Changing the settings means that you modify several parameters of a region:

• geographical projection (e.g. UTM, Latitude-Longitude, Gauss-Krueger, etc),
• geographical extension, i.e. the North/South/East/West limits of the area covered,
• number of columns and number of rows for the data,
• resolution, i.e. the extension divided by the number of rows (N-S resolution), respectively (E-W resolution).

How do we use it? One of several possibilies is to use the GRASS Shell. Open the Toolbox click on Modules List → GRASS Shell.

Synthax

• g.region [rast=name ] [vect=name ] [res=value ] -p -l

Parameters

• [rast=name]= Set region to match this raster map
• [vect=name]= Set region to match this vector map
• [res=value]= Grid resolution 2D (both north-south and east-west)

Flags

• -p= Print the current region
• -l= Print the current region in lat/long using the current ellipsoid/datum

Why care about the region?

The region defines the extension and geometric resolution (pixel size) of the data on which most GRASS (raster) commands work. If the region is set to a smaller extension than that of the map you are working on, display and results of raster processing commands will only show the portion of the map that is contained in that region.

Attention!:

In short, this means that whatever command you use in GRASS, it is always applied only to the data in the current region. So always keep an eye on the region settings!