About Google on a phone - it does have a feature to download areas, so when you don't have service, you still have a map to display. Most phones have separate GPS chips, so in theory as long as they have a good "view" of the GPS satellites, they should work....but..the antennas used are pretty poor, the phones are in places that may partially block satellite reception, etc., etc. - so they use wifi and cell towers to augment. All of this said, in urban areas they can be pretty good. In rural, sometimes good, or maybe not so much or at all. Dedicated GPS units, like Garmin, can be much better at getting several satellite signals, so tend to be more accurate more of the time. I happen to have a fancy GPS on my boat, with a high end antenna...but even that can get lost and confused when I'm out in the wilds.
