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+<!-- meta page description: GRASS GIS Database -->
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+
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+A GRASS GIS Database is simply a set of directories and files
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+with certain structure which GRASS GIS works efficiently with.
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+Location is a directory with data related to
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+one geographic location or a project.
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+All data within one Location has the same cartographic projection.
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+A Location contains Mapsets and each Mapset contains data related to
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+a specific task, user or a smaller project.
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+Within each Location, a mandatory PERMANENT Mapset exists
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+which can contain commonly used data within a Location such as base maps.
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+PERMANENT Mapset also contains metadata related to Location
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+such as projection.
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+When GRASS GIS is started it connects to a Database, Location and Mapset
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+specified by the user.
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+
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+<p>
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+<!-- original drawing: doc/grass_database.svg -->
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+<center>
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+ <img src="grass_database.png" alt="example: nc_spm - highway - elevation"><br>
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+ <i>Fig. 1: GRASS GIS Database structure as visible to the user</i>
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+</center>
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+
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+<!--
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+TODO: Introduction/Rationale/Motivation
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+
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+data format handling separated from analysis
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+
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+organizing the data
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+In geospatial analysis often involves combining data from various sources
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+multiple users
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+-->
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+
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+
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+<h3>GRASS GIS Database</h3>
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+
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+All data for GRASS GIS must be in GRASS GIS Database which is a directory
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+(visible on the disk) containing subdirectories which are GRASS Locations.
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+User can have one or more of Databases on the disk. Typically users have
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+one directory called <code>grassdata</code> in their home directory.
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+In multi-user environment users often have a <code>grassdata</code> directory
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+mounted as a network directory (network file system).
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+For teams, a centralized GRASS DATABASE would be defined
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+in a shared network file system (e.g. NFS).
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+<!-- TODO: above needs some fixes -->
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+
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+<p>
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+GRASS GIS Databases can be safely copied or moved as any other directories.
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+Don't be confused with (relational) databases which are used in GRASS GIS
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+to hold attribute data and might be part of the GRASS GIS Database.
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+From user point of view, GRASS GIS Database with all its data in it
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+is similar to, e.g. PostGIS, database, as it stores all information
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+inside in a specific format and is accessible by specific tools.
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+GRASS GIS Databases is in GRASS GIS often called GISDBASE or DATABASE.
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+
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+
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+<h3>GRASS Locations</h3>
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+
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+Location is a directory which contains GRASS Mapsets which are its subdirectories.
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+All data in one Location have the same projection (coordinate system, datum).
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+Each Location must contain Mapset called PERMANENT.
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+Typically, a Location contains all data related to one project
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+or a geographic area (geographic location or region).
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+Alternatively, Location can simply contain all data in a given projection.
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+
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+<p>
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+GRASS Locations can be safely copied or moved as any other directories.
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+Compressed Location is usually what GRASS users exchange between each other
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+when they want to share a lot of data.
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+For example, GRASS GIS sample data are provided as Locations.
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+
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+<p>
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+Don't be confused with location as a place (file or directory) in a file system.
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+The word location in GRASS Location refers to a location or area on Earth
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+(or whatever is applicable).
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+Users and programmers familiar with relational databases such as PostgreSQL
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+can view Location as an individual database inside the system or a storage area
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+which would be equivalent to GRASS GIS Database. Mapsets in a Locations
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+are like namespaces or schemas inside a database.
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+
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+<!-- TODO: naming limitations and best practices -->
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+
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+
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+<h3>GRASS Mapsets</h3>
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+
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+Mapsets contains the actual data, mostly geospatial data,
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+referred to as maps in GRASS GIS.
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+Mapsets are a tool for organizing maps in a transparent way
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+as well as a tool for isolating different tasks to prevent data loss.
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+
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+<p>
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+GRASS GIS is always connected to one particular Mapset.
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+GRASS GIS modules can create, modify, change, or delete a data only in
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+the current Mapset.
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+By default, only the data from the current Mapset and PERMANENT Mapset
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+are visible. Using
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+<a href="g.mapsets.html"><em>g.mapsets</em></a>
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+module or in GUI other Mapsets can be made visible and seamlessly accessible.
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+All data are available for reading when Mapset is specified explicitly,
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+for example to access map <code>streets</code> in Mapset
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+<code>new_highway</code> user can use <code>streets@new_highway</code>.
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+For maps which are in the current or PERMAENT Mapsets or Mapsets
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+sets as visible (accessible), there is no need to use
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+<code>@mapset</code> syntax.
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+
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+
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+<p>
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+Mapsets are used to store maps related to one project, smaller project,
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+specific task, issue or subregions.
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+In multi-user environment, when a team works together on one project,
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+Mapsets support simultaneous access of several users to the maps
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+stored within the same Location.
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+Besides access to his or her own
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+Mapset, each user can also read maps in PERMANENT Mapsent
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+and in other users' Mapsets when set.
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+However, each user can modify or remove only the maps
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+in his or her own Mapset.
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+
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+<p>
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+Besides the geospatial data, Mapset holds additional data such as
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+color tables (managed e.g. by <a href="r.colors.html"><em>r.colors</em></a>)
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+and the current computational region's extent and resolution
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+stored in a file called <code>WIND</code>
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+and managed by <a href="g.region.html"><em>g.region</em></a>.
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+
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+<p>
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+Mapsets can be copied and moved as directories, however only when it is clear
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+that the projections of both Locations
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+(as reported by <a href="g.proj.html"><em>g.proj</em></a>)
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+match each other. Since this is sometimes hard to to establish,
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+it is recommended to use <a href="r.proj.html"><em>r.proj</em></a>
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+or <a href="v.proj.html"><em>v.proj</em></a> to reproject the data.
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+The files and directories should not be moved or modified directly,
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+but only using GRASS GIS tools.
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+
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+
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+<h3>The role of the PERMANENT Mapset</h3>
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+
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+When creating a new Location, GRASS GIS automatically creates a special
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+Mapset called PERMANENT where the core data for the Location are stored.
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+
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+<p>
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+Since the maps in PERMANENT Mapset are visible from all the other Mapsets,
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+it can be used to store the base maps (base cartography), data common
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+to all projects or needed for different analyses done is separate Mapsets.
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+
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+<p>
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+In multi-user environment, data in the PERMANENT Mapset can only be added,
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+modified or removed by the owner of the PERMANENT Mapset; however, they can be
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+accessed, analyzed, and copied into their own Mapset by the other
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+users. The PERMANENT Mapset is useful for providing general spatial
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+data (e.g. an elevation model), accessible but write-protected to all
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+users who are working in the same Location as the database owner.
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+To manipulate or add data to PERMANENT, the owner can start
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+GRASS GIS and choose the relevant Location and the PERMANENT Mapset.
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+
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+<p>
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+The PERMANENT Mapset also contains the <code>DEFAULT_WIND</code> file which holds
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+the default computational region's extent and resolution values
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+for the Location (which all Mapsets will inherit when they are created).
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+Users have the option of switching back to the default region at any time.
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+
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+
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+<h3>Importing, exporting and linking data</h3>
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+
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+GRASS GIS works only with data which are imported into a GRASS Database,
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+so all data needs to be imported, e.g. by
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+<a href="r.in.gdal.html"><em>r.in.gdal</em></a> or
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+highly convenient <a href="r.import.html"><em>r.import</em></a>,
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+before the actual analysis.
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+Data in GRASS Datable can be exported using for example
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+<a href="r.in.gdal.html"><em>r.in.gdal</em></a> in case of raster maps.
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+
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+<p>
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+For cases when import is not desirable, an option to link external data exists.
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+Projection of the linked data must match the Location's projection
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+otherwise the external data cannot be linked. (Linking data in different
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+projection is not allowed as it would require on-the-fly reprojection
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+which could cause inconsistencies in the data.
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+
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+<p>
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+For example, module <a href="r.external.html"><em>r.external</em></a> links
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+external raster data, so that the data are accessible in GRASS Database
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+as standard raster maps. Similarly for newly created maps,
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+<a href="r.external.out.html"><em>r.external.out</em></a>
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+setups a format and directory where the actual data will be stored,
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+however in GRASS Database the data will be created as standard maps.
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+
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+
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+<h3>Starting GRASS GIS using GUI</h3>
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+
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+After launching GRASS GIS, the startup window will open (Fig. 2).
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+
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+<p>
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+<center>
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+ <img src="grass_start.png" alt="startup window with numbered fields"><br>
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+ <i>Fig. 2: GRASS GIS startup window</i>
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+</center>
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+
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+The startup windows provides these functions:
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+
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+<ol>
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+ <li>Selecting the GRASS GIS Database directory.
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+ <li>Selecting the Location (e.g. a project or area).
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+ See the <em>Location Wizard</em> (4) for creating new Locations.
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+ <li>Selecting the Mapset (a subproject or task).
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+ Creating a new Mapset requires only name.
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+ <li>The <em>Location Wizard</em> for creating new Locations
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+ based for example, on existing georeferenced file or EPDS code.
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+ <li>Start GRASS GIS once you have selected an existing Location and Mapset
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+ or defined a new one. The graphical user interface
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+ <a href="wxGUI.html">wxGUI</a> will open and provide you with a
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+ menu system, map visualization tool, digitizer, and more.
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+</ol>
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+
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+
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+<h3>Starting GRASS GIS using command line</h3>
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+
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+GRASS GIS can be started with given Database, Location and Mapset
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+from the command line. For example, the following will start
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+in a given Mapset with only command line interface:
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+
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+<div class="code"><pre>
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+grass71 -text ~/grassdata/mylocation/mymapset
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+</pre></div>
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+
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+And the following will create the given Location with projection given
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+by the EPSG code and it will start the default interface
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+(GUI or command line):
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+
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+<div class="code"><pre>
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+grass71 -c EPSG:5514:3 ~/grassdata/mylocation
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+</pre></div>
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+
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+See <a href="grass7.html"><em>grass</em></a> command manual for more details.
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+
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+
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+<h3>Creating a New Location with the Location Wizard</h3>
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+
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+The <a href="wxGUI.html">wxGUI</a> graphical user interface provides a
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+graphical <em>Location Wizard</em> which lets you easily create a
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+new Location for your own data. You will be guided through a series of
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+dialogues to browse and select predefined projections or to
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+define custom projections.
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+
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+<p>
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+The most convenient way of using <em>Location Wizard</em> is creating new
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+Location based on a georeferenced file, such as Shapefile or GeoTIFF,
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+or by selecting the corresponding EPSG projection code.
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+In case of using georeferenced file, you are asked whether the data itself
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+should be imported into the new Location.
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+<!-- TODO: some of this should be or already is automatic
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+dialog with checkboxes would be also more convenient than multiple questions -->
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+The default region is then set to match imported map.
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+<!-- TODO: difference rasters versus vectors -->
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+
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+<!--
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+TODO: some notes about resolution and extent would be nice
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+(as well as removing the step from the wizard)
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+
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+this was in the text pointing to some unknown text:
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+* The rules to define the resolution as described above also apply here.
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+* Find below also some rules to define the default raster resolution
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+ for a new Location.
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+-->
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+
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+<p>
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+After defining a new Location, wxGUI starts automatically.
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+<!-- TODO: how GUI start actually works -->
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+If data were already imported, you can add them into the Layer Manager now
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+and display them.
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+More data can be imported into the Location, e.g. using import options in
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+the <em>File</em> menu in <em>Layer Manager</em> or
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+<a href="r.import.html"><em>r.import</em></a>.
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+
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+
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+<h2>See also</h2>
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+
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+<em>
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+<a href="index.html">GRASS GIS 7 Reference Manual</a>
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+<br>
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+<a href="grass7.html">GRASS GIS 7 startup program manual page</a>
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+<br>
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+<a href="http://grasswiki.osgeo.org/wiki/Importing_data">Importing data on GRASS Wiki</a>
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+<br>
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+<a href="r.import.html">r.import</a>,
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+<a href="v.import.html">v.import</a>,
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+<a href="r.external.html">r.external</a>,
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+<a href="v.external.html">v.external</a>,
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+<a href="r.proj.html">r.proj</a>,
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+<a href="v.proj.html">v.proj</a>,
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+</em>
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+
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+<p>
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+<i>Last changed: $Date$</i>
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Vaclav Petras
