The sailors of old typically used flat maps to find their position, so three reference points would suffice. Since GPS devices move in three dimensions, you need a fourth satellite so that you can ...

Devices with paid subscriptions are most often satellite communicators, like the Garmin inReach Messenger Plus, and mapping apps that offer offline maps, like onX Backcountry and Gaia GPS.

Topographic maps and trail mapping are essential for off roading. Satellite communication: If you're going deep into the wilderness, opt for a GPS with satellite communication, like the Garmin ...