Having a GPS receiver is not a panacea for orienteering. The device provides only valuable information that helps to make an informed decision on navigation, tactics of passing obstacles, and in no way cancels the maps and compass, but only complements them well. All GPS devices are small specialized computers that require a detailed study of the voluminous instructions for their use. In order for the device to bring noticeable help on the route, you need to do a lot of preparation work at home. To do this, you need a personal computer with the appropriate software. Here you will find a noticeable number of links to literature, which will have to be mastered. The following is a personal experience of using a GPS receiver in real mountain hiking.
The GPS system consists of three components: a system of control stations, satellite constellation and user properties (GPS receivers).
A satellite constellation includes at least 24 satellites (at the time of writing, there were 31 satellites) placed in orbit so that at least four of them are always visible at any point on the board. This is the minimum amount required by the receiver to determine its coordinates in the mountains. On the plain, if the height is known, three are enough. Really almost always seven satellites and more are visible. A greater number of them increases the accuracy and reliability of the system. As a rule, the system continues to function, even if part of the sky is covered by mountains or buildings, although accuracy may decrease. The determination of coordinates is impossible only in completely deaf gorges or in a dense broad-leaved forest. But in such places, a compass and a map will help you. In highlands there are almost no situations that the device is not determined. Detailed information on the functioning of the system is on the sites.