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North America at night, satellite image. North is at top. Yellow lights mark the major cities. The western coast of the USA is the most brightly lit area, with the urban area of Los Angeles, San Francisco, Seattle and Vancouver (in Canada), all seen. The eastern USA is densely populated and has many major cities. The American Mid-West, which lies between these other two areas, is sparsely populated, with large stretches of plains, deserts and mountains seen as dark areas. The far north is uninhabited, apart from the lights of Alaska (top left). The Pacific Ocean is also dark. Dawn is breaking over the eastern coast of the USA. (KEYSTONE/SCIENCE PHOTO LIBRARY/PLANETARY VISIONS LTD)