The current region dictates the boundaries and resolution of any raster map you create during your work session. For example:
REGION FACILITY
LOCATION: spearfish MAPSET: john
CURRENT REGION: N=4928000 S=4914020 RES=30 ROWS=466
E= 609000 W= 590010 RES=30 COLS=633
PROJECTION: 1 (UTM)
ZONE: 13
You can change region parameters any time with the g.region module. Option 1 of g.region will let you modify bolded region parameters directly:
IDENTIFY REGION
============================= DEFAULT REGION ========
| Default North:4928000 |
| |
| ======= YOUR REGION ======= |
| | NORTH EDGE:4928000____ | |
| | | |
Def. West |WEST EDGE | |EAST EDGE | Def. East
590000 |590010_____| |609000_____| 609000
| | SOUTH EDGE:4914020____ | |
| ============================= |
| |
| Default South:4914000 |
=====================================================
PROJECTION: 1 (UTM) ZONE: 13
Default GRID RESOLUTION Region
100 --- East-West --- 30________
100 -- North-South -- 30________
AFTER COMPLETING ALL ANSWERS, HIT TO CONTINUE
(OR TO CANCEL)
Alternately, you can save or set your region from a region
parameter file, or set your
region from the cellhd information in a raster map or
from a vector map, e.g.:
g.region rast=elevation.dem
You can change cell resolution, e.g.:
g.region res=100
Note that whenever you change any region parameter with g.region, these changes will apply to any subsequent work, although you must d.erase your GRASS monitor to see the effects of the change.
When you start a GRASS session, you will be in the region you ended your previous work session in.
r.mask is an interactive utility which lets you mask out (set to zeroes) any cells in areas you are not interested in. It creates a binary raster file called MASK in your mapset, and this mask remains in effect until you remove it with r.mask. (Or, you can issue the command g.remove MASK.)
Any map you create while you have a mask in place will have zero values in all masked cells. .