[GRASSLIST:5989] Re: a little help for a new user?

[Glynn Clements]

Richard Greenwood wrote:

> > I just downloaded the spearfish data set from 
> > http://grass.baylor.edu/sampledata/spearfish_grass5data.tar.gz, and I have 
> > a few questions.  When I start up GRASS (on Mac OS X), I'm asked for my 
> > location, mapset, and database.  I understand GRASS will always ask me for 
> > this information, but I don't understand how to complete these fields.
> > 
> > So, if I unzip the download and create the directory 
> > /home/grass/spearfish, would it make sense to choose:
> > 
> > LOCATION: spearfish
> > MAPSET:   PERMANENT
> > DATABASE: /home/grass/spearfish
> > 
> > Does it even make sense to create this directory?
> 
> Yup. Every location has a PERMANENT. This would logically hold base maps. 
> As you develop an area, you might add other mapsets like project1 and 
> project2, or Bob and Fred. Maps in the PERMANENT mapset are accessible from 
> all other mapsets within a location.

You shouldn't normally choose PERMANENT as the mapset in the startup
screen. The mapset which you choose there determines where any new
maps will be created. You can always read maps from the PERMANENT
mapset regardless of the current mapset.

AFAICT, the "normal" approach is to use your username as the mapset;
the idea being that, on a multi-user system, each location will
typically have a PERMANENT mapset plus a mapset for each user. Each
user can read maps from either PERMANENT or from their personal mapset
(plus any other mapsets which are selected via g.mapsets), while any
new maps will go into their personal mapset.

With such a setup, each user owns their own mapset, while PERMANENT
will typically be owned by an administrative account. Apart from the
issue of Unix file permissions, GRASS won't let you select a mapset
which you don't own.

In more complex situations, each user may have several personal
mapsets (creating a new mapset requires that you have write permission
on the location; creating a new location requires that you have write
permission on the database directory).

Even on a single-user system, it's preferable to leave PERMANENT
alone, and create any new maps in a separate mapset.

Also, you probably shouldn't include "spearfish" in the database
directory. Each location is a separate subdirectory of the database
directory, and it's normally preferable to have a single database for
all GRASS data, rather than a separate database for each dataset.

-- 
Glynn Clements <glynn.clements at virgin.net>