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1helptext(1)                   Grass User's Manual                  helptext(1)
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5GRASS Quickstart
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Geographic Resources Analysis Support System

8       Commonly  referred to as GRASS, this is a Geographic Information System
9       (GIS) used for geospatial data management and analysis, image  process‐
10       ing,  graphics/map  production,  spatial  modelling, and visualization.
11       GRASS is currently used in academic and commercial settings around  the
12       world,  as well as by many governmental agencies and environmental con‐
13       sulting companies.
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Introduction

16       GRASS data are stored in a directory  referred  to  as  DATABASE  (also
17       called  "GISDBASE").   This directory has to be created with mkdir or a
18       file manager, before starting to work with GRASS.   Within  this  DATA‐
19       BASE, the projects are organized by project areas stored in subdirecto‐
20       ries called LOCATIONs.
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22       A LOCATION is defined by its coordinate system, map projection and geo‐
23       graphical  boundaries. The subdirectories and files defining a LOCATION
24       are created automatically when GRASS is started the first time  with  a
25       new LOCATION.
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27       Each LOCATION can have many MAPSETs. Each MAPSET is a LOCATION's subdi‐
28       rectory. New MAPSET can be added at Grass startup. To remove a  MAPSET,
29       remove   it's   directory   using  your  file  manager  or  by  rm  -rf
30       /path/to/the/mapset_to_delete.
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32       One motivation to maintain different mapsets is to store  maps  related
33       to  project  issues  or  subregions.  Another  motivation is to support
34       simultaneous access of several users to the map  layers  stored  within
35       the  same LOCATION, i.e. teams working on the same project. For teams a
36       centralized GRASS DATABASE would be defined in a  network  file  system
37       (e.g.  NFS).  Besides  access to his/her own MAPSET, each user can also
38       read map layers in other users' MAPSETs, but s/he can modify or  remove
39       only the map layers in his/her own MAPSET.
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41       You can learn more about mapsets from g.mapsets documentation.
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43       When  creating  a  new  LOCATION, GRASS automatically creates a special
44       MAPSET called PERMANENT where the core data  for  the  project  can  be
45       stored.  Data  in  the  PERMANENT MAPSET can only be added, modified or
46       removed by the owner of the PERMANENT  MAPSET;  however,  they  can  be
47       accessed,  analyzed,  and  copied  into  their  own MAPSET by the other
48       users. The PERMANENT MAPSET is useful  for  providing  general  spatial
49       data  (e.g.  an elevation model), accessible but write-protected to all
50       users who are working in the same LOCATION as the database  owner.   To
51       manipulate  or  add  data to PERMANENT, the owner would start GRASS and
52       choose the relevant LOCATION and the  PERMANENT  MAPSET.   This  mapset
53       also  contains  the  DEFAULT_WIND  file, which holds the default region
54       boundary coordinate values for  the  location  (which  all  users  will
55       inherit  when  they  start  using  the  database). Additionally, in all
56       mapsets a WIND file is kept, for storing the current  boundary  coordi‐
57       nate  values  and the currently selected raster resolution.  Users have
58       the option of switching back to the default region at any time.
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Creating a GRASS database

61       To create the GRASS database: Find a place on your disk where you  have
62       write  access  and  that has enough diskspace to hold your decompressed
63       data.  Create a subdirectory that will hold the general GRASS  database
64       (e.g. mkdir /data/GRASSDATA or mkdir /home/yourlogin/GRASSDATA).
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66       Sample data such as the Spearfish sample dataset may be downloaded from
67       http://grass.itc.it/download/data.php and placed in  the  new  database
68       directory.
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70       Click  on  the  "Create  New Location" button, which will take you to a
71       text screen on which you can enter a new location name, and  then  con‐
72       tinue  by  pressing "ESC"-"RETURN" - i.e. press (NOT hold) the ESC key,
73       and then press the RETURN key on your keyboard.
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75       Next you will need to assign parameters to the  location  such  as  the
76       coordinate  system and datum you want to use, the project area's bound‐
77       ary coordinates, and the default resolution for raster data:
78              Start by  chosing  between,  X,Y,  Latitude-Longitude,  UTM,  or
79              "other"  coordinate system. This choice depends on your data and
80              the use you will make of it.  You are then prompted for a single
81              line  of text describing the project area, for example "Topo Map
82              of the Alps".
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84       Next you are requested for some more information about the  projection.
85       Note  that  the  prompts vary from projection to projection, an example
86       follows:
87              (if you chose "D - Other Projection") "specify projection name":
88              "list" gives you the list of all available projections, examples
89              are "tmerc" for Transverse Mercator, "lcc" for Lambert Conformal
90              Conic, "moll" for Mollweide, etc.  specify datum name: again use
91              "list" to get a list of available datums, examples are  "wgs84",
92              "nad27",  "eur79",   etc.  Enter Central Parallel: 0 if you want
93              the Equator as the central parallel Enter Central Meridian: 0 if
94              you  want the Greenwich meridian as central meridian Enter Scale
95              Factor at the Central Meridian Enter plural form of  map  units:
96              for example, meters
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98       The next step is the description of the project area's boundary coordi‐
99       nates and the definition of the default raster resolution:
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101       The default raster  resolution  (GRID  RESOLUTION)  has  to  be  chosen
102       according to your needs. Generally, it is advisable to work in steps of
103       0.25 (0.25, 0.5, 1.75, 2.00, 12.25 etc.). This resolution does not con‐
104       cern vector and site data since these are stored with their exact coor‐
105       dinate values. Note that every raster map may have its own  resolution.
106       You can leave this screen with "ESC"-"RETURN" and then if everything is
107       correct accept the list of parameters that appears.
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109       You will then be back to the startup screen to enter the mapset's  name
110       (if  not  already entered). Another "ESC"-"RETURN" will finally let you
111       leave this screen. This mapset is created within the  new  location  by
112       answering  "yes"  to the next question. The mapset will use the parame‐
113       ters of the location (such as the region and resolution definitions) as
114       its default parameters.
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116       Now  the  project  area, i.e. the location including a mapset, has been
117       created. You have "arrived" in the GRASS system and can  start  working
118       within this new location.
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Geographic Resources Analysis Support System

Introduction

Creating a GRASS database

Further Reading

See also