After our trip to Mojave desert it was a lot of questions about APRS system. I will not re-invent the wheel. There are a lot of info about APRS in the internet.
The good start point here: APRS

my current position here: W6BVB-7

And yes, it is very useful for off-road application!

2001 Trooper LS 3" lift,no more Rancho 9000RX,
no more 4L30E transmission,
ProComp 8" 130W driving lights,
Surco roof rack (modified),
110V power outlet, Viair 380C compressor,
CB/FRS/GPRS/HF/VHF/UHF Radio, 285/75/16 BFG AT/KO.