Tiger README file
Gregg M. Townsend and William S. Evans
July 31, 2000


These programs draw road and street maps from the "TIGER/Line" data
files (1994 or later) of the U.S. Census Bureau.  Two programs are key:

   tgrprep.icn	reformats TIGER/Line data into smaller, more easily
		displayed "line chain" files.

   tgrmap.icn	reads line chain files and displays a map.  Zooming
		and other features are provided.  A subset of the map
		can be saved as either line chains or as a PostScript
		file for printing.

Other programs are useful, though not necessary:

   tgrlink.icn	connects line chains to produce a smaller, faster version
		of the same data

   trgmerge.icn	merges data from multiple line chain files

   tgrtrack.icn creates a line chain file from a GPS track log.

   tgrquant.icn quantize line chain files to simulate a loss of precision.

Four UNIX scripts also manipulate line chain files:

   tgrsort	orders map data from least to most significant.

   tgrstats	counts the occurrences of each type of feature.

   tgrclean	removes insignificant features.

   tgrstrip	removes even more features.

There is a wealth of information in the TIGER files; only some of it is
displayed.  In particular, street names are not displayed, and bounded
regions such as lakes are not filled in.

The Census Bureau has a TIGER page on the World Wide Web:
	http://www.census.gov/geo/www/tiger/
They have an on-line mapping service that is somewhat more sophisticated
than these programs.


TIGER 1998 data is available on-line from the Census Bureau:
	http://www.census.gov/geo/tigerline/tl_1998.html

TIGER 1997 data is available by FTP from the Social Science
and Government Library of the University of California at Berkeley:
	http://sunsite.berkeley.edu/GovData/info/tiger.html

TIGER data is also available on CD-ROM; in the 1998
version, seven discs ($70 each) cover the entire United States.  See:
	http://www.census.gov/mp/www/rom/msrom12l.html

TIGER CD-ROM discs may also be available at your nearest Federal
Depository Library or other major library.  Local data may also be
available from city or county planning offices and the like.



The process of making a map goes something like this:
    * find the appropriate data file; there is one for every county
    * unzip the county file, producing about 17 separate files
    * run tgrprep, using the first two of those files, to make a .lch file
    * run tgrmap, reading the .lch file
    * zoom in on the area of interest
    * save that as a new and smaller .lch file
    * optimize the .lch file using tgrlink  [this step is optional]

The final .lch file can be redisplayed, explored, printed, and so on.


These programs and scripts were developed and tested under UNIX.