If you can't download baltimore.map because your browser treats .map
as a special extension, then try baltimore.mapfile.  They are
identical.

Or you could just download the whole zipfile at
http://cs.jhu.edu/~jason/226/hw10/HW10-DOWNLOAD-FILES.ZIP

For information on how to make your own maps, see the section "The
Data" in the assignment.  This involves downloading a zipfile from the
U.S. Census Bureau website, and running one of the files inside it
through the rt1_to_map script.

If you want to try 6 Degrees of Kevin Bacon, Dan Mallinger has kindly
prepared a file giving some male actors together with their movies.
The file is inside someactors.zip.  It is derived from the male actors
file (no actresses!) at the Internet Movie Database.  Dan says that to
help the graph fit in memory, "only people who appear in 20 movies
from 1980 on are in there."