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Know Your Earth 2.0: Where People Live
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A jewel in the darkness, Chicago appears as a half-moon of light set against the black depths of Lake Michigan in this image captured from the International Space Station. Straight lines of particular brightness illuminate Interstate highways I-55, I-90, and I-94 where they race diagonally into and out of the center city to the northwest, south, and southwest, connecting Chicago with its surrounding region. Smaller roads appear as a lattice throughout the metropolitan area.

The background image was taken by a Defense Meteorological Satellite Program Operational Linescan System. This network of satellites was originally designed to pick up lunar illumination reflecting off clouds at night in order to aid aircraft navigation at night.

City light clusters give an immediate sense of relative city size. Demographers have used nighttime satellite imagery to make estimates of city populations, especially in the developing world where growth can be rapid. Chicago too has grown over the years.

Overall the United States has undergone a steady process of urbanization as a larger and larger percentage of the population has moved towards the cities. Marc Imhoff, a biologist at NASA’s Goddard Space Flight Center, and a team of researchers looked for ways to measure the effects of urbanization on the biological productivity in the U. S. and other countries around the world. They created a method of mapping urbanization on a countrywide scale by using satellite images of the light cities generate at night. With the resulting city lights maps, they have been able to zero in on the impacts urban sprawl has on the food we eat, the air we breathe, and the ecosystem within which we live.

After a great deal of work on the maps of city lights, Imhoff and his group overlaid a map of the United States with other maps showing where the best soils were, where fragile ecosystems existed, and where plant life was the most robust. With such comparisons, the NASA scientists could determine exactly how urbanization is affecting our planet, our natural resources, and even our climate. By repeating the entire process for other countries, they could get an idea of what was happening all over the world.

› Learn about other ways NASA helps to study cities.

Related Images

› Earth’s City Lights
› City Lights at Night along the France-Italy Border

Related Resources

› The Earth Observatory article Bright Lights, Big City describes how NASA scientists use city light data to map urbanization.
› NASA Science News: Lighting Up the Ecosphere
› Beating the Heat in the World’s Cities
› Looking for Lawns

Related Visualization

› 'Earth at Night' rotating globe