[GRASSLIST:6214] RE: labels and TIGER line data?

[John Gillette]

> Even if I'd known that I had to manually create the dig_cats file, I
> don't think I would have been able to figure out the 
> necessary format by
> looking at a dig_cats file in the spearfish location sample.  As shown
> below, the initial number in each line of a spearfish dig_cats file
> appears to be something other than a TLID.  

Greg,

Please note, TLID is NOT a grass term.  TLID is a US Census tiger file
term for the numbers given to the polylines in the tiger file. See the
"Data Dictionary" section of the Tiger Line Technical Documentation:

http://www.census.gov/geo/www/tiger/tigerua/ua2ktgr.pdf  2000 tiger line
or
http://www.census.gov/geo/www/tiger/tiger2002/tgr2002.pdf 2002 tiger line

These will tell you, for example, what character positions to find the 
feature name. 

Grass is flexible about attribute numbers (sometimes also called category numbers
or categories).  They don't have to be sequential, they don't have to start at 1,
and they don't have to be unique.  In the spearfish example, they represent different 
categories of roads.

They could also represent different heights in a contour map, for example.

The author of the v.in.tig.basic program wrote it to have the attribute correspond
to the TLID number so you could relate the line in the map to the tiger data files
in an external database.  This information is in the man page for the v.in.tig.basic
command.
 
> Did you learn that tip by looking at the source code, or is 
> there GRASS
> documentation that specifies the dig_cats file format?  (I'm new to
> GRASS and am not sure if I have complete documentation.)
>

When I started, I used "FREC 682: Spatial Analysis " 
at http://www.udel.edu/johnmack/frec682/ as a tutorial.

This, as well as lots of other info, is referenced on the
"GDP - GRASS Documentation Project" page at 
http://grass.itc.it/gdp/index.html

(From <main page>, find "First Time User?"
   From <Welcome, First Time Users of GRASS!> page, find "Tutorials")

I recommend:

M. Neteler, H. Mitasova, 2002. Open Source GIS: A GRASS GIS Approach.
 464 pages, Kluwer Academic Publishers, Boston, Dordrecht, ISBN 1-4020-7088-8.

GRASS tutorial project, especially Part III of the full tutorial: 
 GRASS in 10 minutes - Quick Intro for Newbies 

GRASS 5.0.x Programmer's Manual (PDF) 

AND, browse the directories and look in the files. Understanding where things are
and how its stored will be helpful.

John