Before we had airplanes and satellites, people went around measuring the distances between objects on the land. Map makers took these measurements and made maps on the Earth's surface.

For the past hundred years, astronomers have been measuring the distances to groups of stars and their directions. Astronomers have used these measurements to make illustrations of the general shape of the Milky Way.

Is it perfect? No, astronomers are still discovering features of the Milky Way, such as the wave in the disc.