Urban areas are growing. But by how much? Satellite imaging can help us monitor urban growth by allowing precise measurements of urbanization patterns over time. NASA researchers used Landsat pictures of 30 randomly-selected mid-size cities around the world from 1990 and 2000 to study city size changes. This will allow for better estimates of urbanization and land use around the world, which in turn is critical for better climate modeling.
These three images show the city of Chengdu in 1990, in 2000, and a combined map, with yellow representing urban areas in 1990 and orange showing the areas of new growth.
Mid-size cities, with populations ranging between 1 and 5 million, were chosen over mega-cities because the somewhat smaller urban areas are growing faster, and may have a greater overall impact on the global climate.
When the cities were compared, three common spatial patterns became clear. First, land developments have formed in clusters outside the city. While fairly common in the U.S., Schneider noticed this trend in large cities of China and India as well. Second, there are a number of cities where growth has occurred along roads leading out of the city. This trend poses challenges both to city managers and governments who must provide water, sewage, adequate housing, schools and health care services to dispersed people, and to the citizens, who face increasingly difficult commutes. Finally, Schneider found scattered, patchy development around cities, with less structure than the first two trends. This is the first time actual data have been used to confirm theories made by urban researchers during the last century.
The pictures are fascinating (even while being a bit alarming).
As a bonus, the page gives a link to NASA's Earth Observatory picture archive. I could fill my hard drive with these images...
