Urban Areas

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Megacities (cities with more than 10 million people) are increasing in number as the global human population continues to become more urban. By the end of 2030, three-fifths of the world population will be living in urban areas (Brennan 1999). Much of this urban growth occurs outside defined city boundaries and the resulting expansion of urban or "built-up" areas can be readily observed from orbit.

The database of astronaut photographs taken since the 1960s offers important baseline data for comparing and calculating the increases in urban areas (Robinson et al. 2000a).


Las Vegas, 1973


Photograph of Las Vegas, Nevada, taken from the Skylab in 1973 (SL3-28-599).


Las Vegas, 1996

Crew Earth Observations on the Space Station will focus on documenting the growth of the largest and fastest growing cities around the world.

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Photograph of Las Vegas, Nevada, taken from the Mir Space Station in 1996 (NM22-725-34).

Growth of Las Vegas3.
As measured from these two photographs, the built-up area around Las Vegas went from 206 square km in 1973 to 628 square km in 1996, an increase of 204 percent. The human population grew from 273,000 to 1.1 million during that time.