[GRASS-user] new user question about mapsets, locations, and coordinate systems

[Michael Barton]

On Dec 9, 2008, at 10:00 AM, <grass-user-request at lists.osgeo.org> <grass-user-request at lists.osgeo.org 
 > wrote:

> Date: Mon, 08 Dec 2008 21:04:52 -0800
> From: mtnbiketrail at zzz.com
> Subject: Re: [GRASS-user] new user question about mapsets, locations,
> 	and	coordinate systems
> To: hamish_b at yahoo.com
> Cc: grass-user at lists.osgeo.org
> Message-ID: <493DFC74.5050003 at zzz.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Thanks Hamish,
> What I meant was: Is each LOCATION typically a different project?(one
> LOCATION for ex. for Ohio, and another unrelated LOCATION for Utah.
> LOCATIONS do not ever cross or mix with each other? And I guess on the
> URL you gave me on the wiki site, that is a yes.
>
> I will try and recreate the ESC+ENTER problem. I would try and  
> create a
> new location and use create coords option and it would never jump to  
> the
> next config screen, just back to the LOCATION/MAPSET/DATABASE window.
> That happened at least three times, but I'm new. I was following what
> the docs said, and I would never get to the next screen the doc  
> described.
>>
>>
>>> For the DATABASE parameter, is GRASS smart enough to add on
>>> the LOCATION directory.
>>>
>>
>> ? not sure I understand the question. a single "database" (where  
>> you keep
>> all your grass data) can contain many locations.
>>
>>

There have been a number of good answers, so I haven't wanted to  
confuse things by adding more. But I guess I'll try to field the first  
part of this.

The GRASS GIS Database (i.e., not a table of attribute values for a  
particular map) is simply a directory/folder where GRASS data files  
are stored. You can have more than one GRASS GIS Database, but it is  
probably simpler if you are a new user to simply keep all your GRASS  
GIS data in one place. Many of us use the unimaginative name of  
"grassdata" for such a directory/folder. You'll need to tell GRASS in  
the startup screen which directory/folder you are using as a GIS  
Database. You only need to do this once unless you change the name or  
put GRASS files somewhere else.

GRASS stores information about your GIS database and other things in a  
file named .grassrc6 (for GRASS 6.0-6.4) and currently in .grassrc7  
(for the in-development GRASS 7).

Within your GIS Database directory/folder, are one or more other  
directories/folder that we call "locations". Each location stores GIS  
data for a single, defined spatial reference system (SRS). For  
example, if you have defined a location for a UTM projection in Zone  
12 with the WGS84 datum, then all the GIS data in that location needs  
to be in UTM Zone 12 WGS84. Within a location, you can also define the  
default "extents"--the default spatial boundaries (NSEW) of your data.

You can have more than one location defined for the same SRS, but you  
cannot GIS data in more than one SRS within a single location. That  
is, you can have multiple locations defined for UTM, Zone 12, WGS84.  
But you cannot have data organized in UTM Zone 12 and UTM Zone 11 in  
the same location. GRASS makes it easy to reproject from one location  
(and SRS) to another location (and SRS).

Within each location, there are yet more directories/folder called  
"mapsets". These are simply places where the actual GIS data are  
stored. You always must have a default "PERMANENT" mapset in every  
location. You can create additional mapsets to organize your work but  
this is not necessary. The data in all mapsets within a single  
location must be in the same SRS. That is, within a single location,  
you cannot have a UTM zone 12 mapset and a UTM zone 13 mapset.

I hope that this helps.