By Dan Shapley
U.S. population continues to rise, and its centers shift south
The U.S. population centers are shifting south. Seven of the 10 largest cities are within 500 miles of the Mexico border, whereas in 1910, the largest cities were within that distance from the Canadian border. Further, 27% of Americans now live in cities -- down from 27.5% in 2000. In other words, suburbia is still on the rise. Population is one of the least-touched environmental issues, but it's at the heart of all of them. The raw numbers of people on Earth have everything to do with how much land is needed to house and grow food for us, how much water we consume, how much energy we need to keep society running, and to what degree we extract non-renewable natural resources. How we live -- where we build out our cities, and how we keep them running -- are the critical questions that mayors around the country have been addressing with increasingly bold and optimistic sustainability plans. As the population continues to increase, these city plans will be increasingly important, according to a story in the June 28 USA Today.