The world's population is nearly 7 billion, about half are urban dwellers. In less than 20 years, experts predict that some 5 billion people will live in cities.
Already, there are at least 21 mega-cities, those with populations in excess of 10 million - among them Tokyo, Seoul, and New York. According to the United Nations Population Fund, though, most future urban growth will take place in smaller towns of Asia and Africa, which have fewer resources to ...