The wifi version does not have GPS, but it can get a reasonable fix from phone masts while on the ground.
Is this true? I've never had my hands on a Wifi-only iPad, but I have always understood that the Wifi-only iPad, only did Wifi and Bluetooth. No GPS, no 3G or any other type of cellular protocol. So presumably it can't receive the signals of any phone mast, and has no way of knowing where it is based on that data. With the possible exception of using a database of Wifi Access Points and their location.
It does seem to have a digital compass though, for what it's worth.
Apple - iPad - View all the technical specifications.