in order to provide a truly global coverage of the Earth from space, including the polar regions, a minimum of just 4 satellites is required. Placed in precise 63.4 degree supersynchronous orbits, one satellite can be in view from any point at any time..... Conversely, in order to guarantee continuous communications with any one satellite from Earth, at least three control stations spaced evenly around the Earth along the orbital plan are necessary for high Earth orbit and above altitude satellites and a minimum of 16 control stations for low-earth orbit ones.
(Source, Dolman, Astropolitik, p 81.)
Can someone help with the intuition here? Why 4 satellites for the 63.4 degree orbit? Why 16 control stations for LEO? Why 3 control stations for high earth orbit?