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 are now zeroing in on the impacts urban sprawl has on the food we eat, the air we breathe, and the ecosystem within which we live. Urbanization in any country generally begins when large-scale commerce takes root and most new jobs are to be found in the factories and financial centers in cities. In the United States, urbanization began to occur roughly around the turn of the last century. Since then, the percentage of people living in the United States in urban areas has risen from 39 percent to more than 73 percent, according to the U.S. Census Bureau.
Urban areas are colored red, while peri-urban areas are colored yellow.
From decade to decade, the amount of rural land that has been consumed by urbanization is enormous. This would be the equivalent of converting half of Ohio into one big subdivision in a ten-year period, according to the World Resources Institute. Urbanization is not just an issue in the United States. Right now, researchers estimate that worldwide movement towards cities is growing at three times the rate of population expansion worldwide. Only a third of the planet's population lived in urban areas ten years ago.