GPS is calculated from signals from a range of satellites far above us in orbit in space. It's not like cellular towers with coverage. There are no real remote areas with GPS - some areas and times of day will have less satellites overhead so calculating a position will be harder. There's more and more of these satellites (from usa, russian, eu, china etc) and modern chips will try calculate position from the signals from many of them rather than one "species"

But yes, remote areas will have less mapping imagery quality because they are remote and uninteresting and don't have roads or people or companies to buy ads on the map. They will buy cheaper imagery in remote areas.