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

Satellite altitude affects what the spacecraft can see, how fast it moves, and how it communicates with Earth. GPS satellites orbit in medium Earth orbit at about 20,200 km, where they can provide stable global timing and positioning coverage. Communications satellites often use geostationary orbit at about 35,786 km so they appear fixed over one point on Earth and can continuously serve the same region. Earth observation satellites are usually much lower, often a few hundred kilometers up, because low orbit gives sharper images and more detailed measurements. Choosing the right orbit is therefore a trade-off between coverage, resolution, and mission purpose.