Tiger README file
Gregg M. Townsend
October 26, 1995


These programs draw road and street maps from the "TIGER94" data files
of the U.S. Census Bureau.  Two programs are key:

   tgrprep.icn	reformats the data into smaller, more easily displayed
		"line chain" files.

   tgrmap.icn	reads a line chain file 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.

Another program is useful, though not not necessary:

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

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.


TIGER94 data is available from the Census Bureau on CD-ROM; six discs
cover the entire United States.  Each CD-ROM also includes documentation
of the file formats.  The discs are $250 each; telephone +1 301 457 4100.

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


At this writing the six CD-ROMs are available on-line via NFS or FTP
over the internet from a CD-ROM farm at the University of California
at Berkeley.  For details see their page on the World Wide Web:
	http://cedr.lbl.gov/cdrom/doc/cdrom.html
Be sure to get the *1994* data.  Older data is in a different format.

CD-ROMs may also be available at your nearest Federal Depository Library.
Check with nearby research universities or big-city public libraries.
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 15 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.
