The Earth Observatory article, “Bright Lights, Big City”, describes how NASA scientists use city light data to map urbanization.
This remarkable image is actually a composite of hundreds of images created using satellite data collected at night. Cities tend to grow along coastlines and transportation networks. The United States interstate highway system appears as a lattice connecting the brighter dots of city centers. In Russia, the Trans-Siberian railroad is a thin line stretching from Moscow through the center of Asia to Vladivostok. Even more than 100 years after the invention of the electric light, some regions remain thinly populated and unlit. Antarctica is entirely dark. The interior jungles of Africa and South America are mostly dark, but lights are beginning to appear.