Earth's City Lights : This image of Earth’s city lights was created with data from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS). Originally designed to view clouds by moonlight, the OLS is also used to map the locations of permanent lights on the Earth’s surface. The brightest areas of the Earth are the most urbanized, but not necessarily the most populated. Cities tend to grow along coastlines and transportation networks; even without the underlying map, the outlines of many continents would still be visible. The Nile River, from the Aswan Dam to the Mediterranean Sea, is another bright thread through an otherwise dark region.