Why do satellites need to orbit at different heights for GPS, communications, and Earth observation?

Orbit height affects what a satellite can see and how quickly it can send data. GPS satellites sit in medium Earth orbit, about 20,200 km up, so they can provide wide global coverage with manageable timing accuracy. Communications satellites often use geostationary orbit at about 35,786 km, where they appear fixed over one point on Earth. Earth-observation satellites usually fly much lower, often a few hundred kilometers up, because lower altitude gives sharper images and faster revisits of the same area.