Generally the portable GPS units don´t have enough memory for a map of the whole world with a satisfying detail level (and you can´t your own either). I agree with Don. IMO using a GPS with paper maps and compass is preferable to GPS units with maps. The paper maps offer more detail and they don´t depend on battery power. When you use a PDA , I´d recommend a map program for that. I have a Palm and a Psion and both work decently with my GPS. I never go without a paper map when I´m not familiar with the area. My preference would definitly be maps, compass, GPS in that order.