navi systems for offroading
 

I'm wanting a navigation system. But I want one that is more for off the beaten path tracking. I'd be really impressed if I could find one that could upload topographical maps and trail maps for national parks. Having one for daily driving around town is a waste of my time. Does anyone know of a navi system of this type? Or maybe a hand held unit that can be plugged into and dash dvd system or something like that?