Basic concept of GPS Hi There are two different issues with the introduction The first is style this is supposed to be a very easy to read introduction The description as intersecting spheres is covered in much detail later in the article Since the article is already very long perhaps another description is not needed in the introduction The second issue is the number of satellites needed This is 3 with an accurate clock a ns or so will suffice This gives the distance to 3 satellites which is enough to determine position These will be 2 solutions but only one can be close to the surface of the Earth so this is not a practical problem With 4 satellites you need only a crude clock provided your hardware measures the 4 satellites at almost the same time This allows you to solve for x y z and t See any GPS textbook for the details of how this is done