Ubuntu Manpage: Geographic Resources Analysis Support System

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. Graphical startup of GRASS GIS

For text-based startup see below.

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.

See to directly download a sample LOCATION into the DATABASE.

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.

Download a sample LOCATION
In the "Location Wizard" there is also a Download button that allows you to directly download a
ready-to-use LOCATION into the DATABASE. You can choose among different sample LOCATIONS that are
currently available at the Download section in the GRASS GIS website.

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" MAPSET
When creating a new LOCATION, GRASS GIS 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
       https://grass.osgeo.org/download/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).

5. Text-based startup and location creation

       GRASS  GIS can be run entirely without using the graphical user interface.  For a first time startup, the
       following steps have to be followed:

       1      Create the GRASS GIS  database  directory  (with  a  file  manager;  or  on  command  line:  mkdir
              /home/user/grassdata

       2      Create a new location, including it’s default PERMANENT mapset, without entering the new location:

           •   Using an EPSG code:
                grass78 -e -c EPSG:32630 /home/user/grassdata/mylocation

           •   Using a georeferenced raster or vector file:
                grass78 -e -c MyGeoReferenceFile.tif /home/user/grassdata/mylocation

       3      Create new mapset within the new location and launch GRASS GIS within that mapset:
               grass78 -c /home/user/grassdata/mylocation/mymapset