# GRASS Help System

## THE DEFAULT WINDOW

GRASS commands can be used to modify the settings of the user's current geographic region. This settings of this region define the geographic boundaries, map projection, coordinate system, and resolution of data sets. GRASS commands commonly ignore data falling outside of this region. For example, when the user digitizes with v.digit, only those areas of the map that fall inside the user's current geographic region will be saved to the vector file produced by "v.digit". When the user displays data to the graphics monitor, only map areas within the user's current geographic region are displayed, in the resolution, map projection, and map coordinates given by the current region settings. When the user runs raster data analysis programs like r.weight on map layers, only those map areas that fall inside the user's current geographic region will be analyzed and included in the resultant raster map layer created by "r.weight". When the user prints map output, current geographic settings are also used. Current geographic region settings are stored in the "WIND" file under the user's current mapset.

Default Geographic Region Settings:
If the user does not explicitly modify his current region settings, GRASS will use the default settings established when the user's current location was first set up; these are stored in the DEFAULT_WIND file under the PERMANENT mapset and copied to the file "WIND" in the user's own mapset. The geographic boundaries described in a location's "DEFAULT_WIND" file should therefore be large enough to encompass all of the map data contained in any of the mapsets under the same location. Its data resolution should also be sufficiently fine for data extraction purposes. Note also that all mapsets under the same location should use the same map coordinate system and projection.

In previous GRASS releases, the geographic region definition was referred to as the "geographic window"; the latter term is now obsolete.

Notes About Geographic Region Settings:
The user may define geographic regions for tape extraction, digitizing and map development, analysis, display, and printed output. The geographic settings that become the user's "current geographic region" settings are stored in the "WIND" file under the user's current mapset. The user can alter these settings using the g.region program, or simply edit this file using a text editor like "vi". The user may wish to use different settings for different purposes, and frequently alter the current region settings. The user can store former region settings in files stored under the "windows" directory kept under the user's current mapset, for possible later use as the user's "current region settings".

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Automatically created on: Mon Apr 4 09:21:45 2005