I'm just taking a shot here, but you may be looking for a scanner that can hook up to a GPS unit so that it can tune in frequencies based on your location. If that is the case, you need to look at the Uniden Home Patrol - it can hook up to a GPS (not included) via a cable and program your listening based on your location. Of course that unit doesn't have to be hooked to GPS, you can put in your zip code or city and listening range to have the radio detect what you want to listen to.
I own both a Pro-106 (similar to PSR 500 and 600) as well as PSR-800 (just bought it and LOVE it!!), and neither radio can be hooked to GPS unit as far as I know.
Happy hunting and scanning...feel free to ask as many questions as you like - this is the place to get answers from some very nice and experienced people.
Bob