Ubuntu Manpage: Geographic Resources Analysis Support System

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GRASS GIS Quickstart

Geographic Resources Analysis Support System

       GRASS  GIS,  commonly referred to as GRASS (Geographic Resources Analysis Support System),
       is a free Geographic Information System (GIS) software used for geospatial data management
       and   analysis,   image   processing,  graphics/maps  production,  spatial  modeling,  and
       visualization. GRASS GIS is currently used in academic and commercial settings around  the
       world,  as  well  as by many governmental agencies and environmental consulting companies.
       GRASS GIS is an official project of the Open Source Geospatial Foundation (OSGeo).

1. Startup of GRASS GIS

After launching GRASS GIS, the startup screen will open:

Selecting the GIS Database directory
GRASS data are stored in a directory referred to as DATABASE (also called "GISDBASE").
This directory has to be created with a file manager or the mkdir command, before starting
to work with GRASS. Within this DATABASE, the projects are organized by project areas
stored in subdirectories called LOCATIONs.

Selecting the LOCATION (a project)
A LOCATION is defined by its coordinate system, map projection and geographical
boundaries. The subdirectories and files defining a LOCATION are created automatically
when GRASS is started the first time with a new LOCATION. It is important to understand
that each projection stays in its own LOCATION.

See the "Location Wizard" to easily create a new LOCATION from scratch from a geocoded
file, by defining the parameters or by selecting the corresponding EPSG projection code.

Selecting the MAPSET (a subproject)
Each LOCATION can have many MAPSETs. Each MAPSET is a LOCATION’s subdirectory. New MAPSET
can be added at GRASS startup (see related button).

Location Wizard
The "Location Wizard" let’s you easily create a new LOCATION. You will be guided through a
series of dialogues to browse and select predefined projections (also via EPSG code) or to
define individual projections. You can also create new LOCATION easily from a
georeferenced data file (e.g., SHAPE file or GeoTIFF, see below). Find below also some
rules to define the default raster resolution for a new LOCATION.

Start GRASS
Once you have selected an existing LOCATION/MAPSET or defined a new one, you can enter
GRASS. The graphical user interface wxGUI will open and provide you with a menu system,
map visualization tool, digitizer, and more.

2. Background: GRASS GIS Location structure

A LOCATION is simply a set of directories which contains the GRASS data of a project.
Within each LOCATION, a mandatory "PERMANENT" MAPSET exists which contains projection
information and some more definitions. It can be used to store the base cartography in it
as "PERMANENT" is visible to all users accessing a LOCATION.

Fig. 1: GRASS GIS 7 location structure

Creating and maintaining MAPSETs
One motivation to maintain different MAPSETs is to store maps related to project issues or
subregions. Another motivation is to support simultaneous access of several users to the
map layers stored within the same LOCATION, i.e. teams working on the same project. For
teams, a centralized GRASS DATABASE would be defined in a shared network file system (e.g.
NFS). Besides access to his/her own MAPSET, each user can also read map layers in other
users’ MAPSETs, but s/he can modify or remove only the map layers in his/her own MAPSET.

You can learn more about mapsets and how to seamlessly access maps found in another MAPSET
of the same LOCATION in the g.mapsets documentation.

The role of the "PERMANENT" LOCATION
When creating a new LOCATION, GRASS automatically creates a special MAPSET called
PERMANENT where the core data for the project can be stored. Data in the PERMANENT MAPSET
can only be added, modified or removed by the owner of the PERMANENT MAPSET; however, they
can be accessed, analyzed, and copied into their own MAPSET by the other users. The
PERMANENT MAPSET is useful for providing general spatial data (e.g. an elevation model),
accessible but write-protected to all users who are working in the same LOCATION as the
database owner. To manipulate or add data to PERMANENT, the owner would start GRASS and
choose the relevant LOCATION and the PERMANENT MAPSET. This mapset also contains the
DEFAULT_WIND file, which holds the default region boundary coordinate values for the
LOCATION (which all users will inherit when they start using the database). Additionally,
in all mapsets a WIND file is kept, for storing the current boundary coordinate values and
the currently selected raster resolution. Users have the option of switching back to the
default region at any time.

3. Creating a GRASS Database with Sample Data

       To create the GRASS database:

       1      Find  a  place  on  your  disk where you have write access and that has enough disk
              space to hold your spatial data.

       2      Create a subdirectory that will hold the general GRASS database (e.g. using a  file
              manager or with mkdir /data/grassdata or mkdir /home/yourlogin/grassdata).

       Sample  data  such  as  the  "North  Carolina"  or  the "Spearfish" sample datasets may be
       downloaded  from  http://grass.osgeo.org/download/sample-data/  and  the  compressed  data
       package(s) extracted into this new database directory.

       Now  you  are ready to select a sample dataset in the GRASS GIS startup screen (see above)
       and start the session.

4. Creating a New Location with the Location Wizard

       The wxGUI graphical user interface provides a graphical "Location Wizard" which  lets  you
       easily  create  a  new  LOCATION  for  own  data.  You  will be guided through a series of
       dialogues to browse and select predefined projections (also via EPSG code)  or  to  define
       individual  projections.  The rules to define the resolution as described above also apply
       here.

       Hint: You can create new LOCATION easily from a georeferenced data file (e.g., SHAPE  file
       or  GeoTIFF file with the related metadata properly included).  In this case you are asked
       whether the data itself should be imported into the new LOCATION. The  default  region  is
       then set to match imported map and the GRASS GIS session is opened.

       After  defining  new LOCATION, wxGUI starts automatically.  If data were already imported,
       you can add them into the Layer Manager now and display them. If your  LOCATION  is  empty
       you  can  import your data from the menu: Go to "File" -> "Import raster/vector data" (see
       also the related Wiki page on Importing data).