Does the iPad have a built-in GPS (Global Positioning System) receiver?
The 3G version does; the Wi-Fi version does not. The 3G-capable iPad uses the same Assisted GPS technology used in the iPhone 3G and 3GS. (Despite how it sounds, “Assisted GPS” is not a lesser form of GPS. “Assisted” means the device can use other cues–such as the location of nearby cellular towers or Wi-Fi networks–to speed up the initial GPS “fix” compared to using the GPS circuitry alone.) The Wi-Fi version uses the same Wi-Fi-based location finding system as the original iPhone. If it can spot some familiar Wi-Fi base stations, it can figure out where you are.