[GRASSLIST:2975] Re: Question about setting up mapsets and importing data

Roger Miller rgrmill at rt66.com
Wed Jan 23 15:48:42 EST 2002

On Wed, 23 Jan 2002, Keene Haywood wrote:

> I just want to make sure I am clear about setting up files for a project
> in Grass.
> I undertand that Grass will access a database of map files.  These are
> organized according to location.  Within the location are mapsets of
> specific areas(data layers) within the location region.  

The grass database is a tree structure.  The lowest level is the database,
and a grass installation may have several databases.  The lowest level
branching from the database is called a location.  The location contains
additional branches called mapsets.  Data layers are branches from the

Locations are associated with a projection and a default region.  Each
mapset that branches from a single location shares the same projection,
but a different region can be specified for each mapset.

I find the names a little confusing, as the "location" only specifies the
projection and a default region; the actual regional coverage is specified
at the level of the mapset.

> When accessing files in this mapset of data layers, does Grass know what
> the projection, coordinates, etc. are, or do you have to set this up
> manually.  If so, where in Grass does one do this?

GRASS knows.  However, the default region (part of the location
specification) may not have much to do with the actual location of data
stored in a mapset.  You generally have to reset the region in each mapset
in order to get a useful coverage.  That can be done with g.region, or
more interactively with d.zoom.
> For example, can I put some raster GIS files (DOQ's in .tif format) and
> then expect Grass to read the geographic info. files for these images and
> display them or do you set up the parameters (coordinates, etc.) first.  

A little of both.  You have specify the projection and a default region
when you create a location.  You can then set the actual region used in a
mapset by (for instance) using the command "g.region rast=<raster map
name>" and that will set the region based on the limits of the raster map.
You can't use that mechanism to define the projection. However, I think
that r.in.gdal can create new locations based on projection information
stored in some file formats.  I haven't done that myself.

Roger Miller
Lee Wilson and Associates

More information about the grass-user mailing list