GPS has nothing to do with cell signal. GPS is it's own signal from satellites that your phone has no problem receiving in a place like Iowa. In fact Iowa has a lot of things going for it to enhance GPS receivership - it's flat so you can see most of the sky, it's open - there's just not a lot of vegetation to absorb the signal coming from overhead (e.g. trees), its in the middle of the US which means there's always going to be 4 or 5 satellites with a line of sight to your phone.