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A view of the world by night. The brightest areas of the Earth are the most urbanized, but not necessarily the most populated. (Compare Western Europe with China and India.) Cities tend to grow along coastlines and transportation networks. The US 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 eastward. The Nile River, from the Aswan Dam to the Mediterranean Sea, is another bright thread through an otherwise dark region. Image courtesy of NASA.