Preparing Input Data Sets

The GRASS GIS program will be used to process and store your set of spatial data layers associated with a project. This module assumes that a GRASS data set has already been created with a PERMANENT mapset containing at least a DEM. This needs to be created only once at the beginning of a project to store initial data.

Set the geographic region

A region refers to a geographic area with some defined boundaries, based on a specific map coordinate system and map projection. In GRASS, each region also has associated with it the specific east-west and north-south resolutions of its smallest units (rectangular units called "cells").

The region's boundaries are given as the northernmost, southernmost, easternmost, and westernmost points that define its extent. The north and south boundaries are commonly called northings, while the east and west boundaries are called eastings.

You need to set the geographic region for your personal mapset. For now, this will be the same as the DEM. Set the region with:
grass> g.region rast=<dem>

To find out the settings of the current region:
grass> g.region –p

This will tell you the projection, zone, datum, ellipsoid, N/S/E/W coordinates, resolution, and number of rows and columns of your DEM.