Michael Mehaffy also points out that not everyone enjoys life in the big city.

MICHAEL MEHAFFY: "Not everybody kind of wants to live in a super high-density city. I think people from different political persuasions, and all walks of life are getting more interested in more connected urban environments, and that isn't necessarily just big cities.”

In this world of seven billion people, a United Nations report says the population balance has tipped in favor of cities and away from rural areas. But it also says there is no easy answer to the question of what exactly a "city" is in twenty-eleven. "Governments and urban areas themselves define 'city' in numerous ways and their boundaries can shift, sometimes for political, demographic or economic reasons."

The U.N. Population Division calls Tokyo and other huge population centers "urban agglomerations." Under that definition, Tokyo is the world's largest urban area. Almost thirty-seven million people live there -- more than one-fourth of Japan's population. Delhi is second, with twenty-two million people, then Sao Paulo and Mumbai. Next are Mexico City; the New York-Newark, New Jersey, area; Shanghai; Kolkata; Dhaka and Karachi.

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SHIRLEY GRIFFITH: Most Americans buy their food in supermarkets. But more and more people are looking for other sources of fresh produce, like farmers markets or their own gardens. Some people are even exploring the world of wild plants. Tim MacWelch is a forty-year-old expert in finding food in the wild. He started the Earth Connection School in nineteen ninety-seven. The business is located in Fauquier County, Virginia, southwest of Washington.