Notes:
APRS Protocol Specification. Lots of very good detail on the content of APRS packets.
ftp://ftp.tapr.org/aprssig/aprsspec/spec/aprs101/APRS101.pdf
Bob Bruninga's APRS documentation. Good overveiw and lots of details with very good discussion of concepts in aprs.
http://www.usna.navy.mil/~bruninga/APRS-docs
SOCAL Digipeater Guidelines
http://www.cal-net.org/aprs/socalaprs.htm
Findu.com – Map station locations on the web.
http://map.findu.com/callsign