GPS, or Global Positioning System, is a modern system that permits navigation using radio in a significantly different method than that of other methods discussed previous. While all previous systems require only some sort of equipment in the air, and a ground station, GPS requires one additional station - or rather, twenty four of them, orbiting our little planet.

GPS provides a level of accuracy that was unheard of prior to its use - and all it simply requires, as far as a pilot (or any user,  GPS is used everywhere!) is concerned, is a receiver that has an unobstructed view of the sky. GPS is not subject to weather conditions, it isn't degraded by mountainous conditions, and range is inapplicable. 

"Expandable 24-Slot satellite constellation, as defined in the SPS Performance Standard."
https://www.gps.gov/systems/gps/space/