GPS

How the fuck does it work?

Say you buy some handheld gps device, do you have to pay anything to get signals, like a cellphone, or is it free?

Does it work everywhere in the world? How good is the update rate? And doesn't it eat battery power like hell?

But I was thinking, in order to show where you are on a map, the device would have to have the map already packed into the memory, right? It doesn't download the map from a satellite, does it?

So does such a device really have maps from the whole world programmed into it?