IN HER BOOK Cities and the Wealth of Nations, author and economist Jane Jacobs declared that cities were "the root of all economic expansion." Economic growth, Jacobs determined, came from cities replacing products that were imported from other cities with products manufactured within the city. For this single reason Jacobs believed that cities were the engines of the economy.

But cities are more than the economic engines that churn out products from factories. They are the homes of millions of people. Social philosopher Lewis Mumford observed in The Culture of Cities that "the city is the form and symbol of an integrated social relationship: it is the seat of the temple, the market, the hall of justice, the academy of learning. Here in the city the goods of civilization are multiplied and manifolded; here is where human experience is transformed into viable signs, symbols, patterns of conduct, systems...