Two hundred forty-three million Americans crowd together in the 3 percent of the country that is urban. Thirty-six million people live in and around Tokyo, the most productive metropolitan area in the world. Twelve million people reside in central Mumbai, and Shanghai is almost as large. On a planet with vast amounts of space (all of humanity could fit in Texas - each of us with a personal townhouse), we choose cities. Although it has become cheaper to travel long distances, or to telecommute from the Ozarks to Azerbaijan, more and more people are clustering closer together in large metropolitan areas. Five million more people every month live in the cities of the developing world, and in 2011, more than half the world's population is urban.
- From Triumph of the City: How Our Greatest Invention Makes Us Richer, Smarter, Greener, Healthier, and Happier by Edward Glaeser