There is a map available at:
http://aprsworld.net/data/igate-hops/This shows how many hops were needed before an APRS packet reached an Internet gateway. The map displayed is for California, but the author says he will make more maps of other areas if there is interest.
Some interesting features: Most of us can get by with just WIDE-2-2, or RELAY,WIDE2-2 paths in most of California. The map also shows where the dead zones are (Barstow to Vegas, Eastern Sierras, etc).