Observers of the city frequently address it as a living thing. The critic Jane Jacobs said that cities, like the life sciences, present "problems of organized complexity," where different factors exist "simultaneously and in interconnecting ways." Like an organism that takes on a new shape as it absorbs different molecular elements, so the city's structures and avenues expand and contract according to its residents' number and need. Our environment responds to us, and we are in turn shaped by its response as we receive new information about the consequences of our actions.
Humanity will turn a corner next year when its majority leaves rural areas for cities, the United Nations tells us. In 1950, two of every three of the world's inhabitants lived in the countryside: By 2030, that figure will be reversed. These changes are most acute in the developing countries of Africa and Asia, as they climb the arc of rapid industrialization that Europe and the Americas traveled in the late 19th century. But because the world's population is today more than four times that of the industrial age, these new "megacities" and "hypercities" dwarf our historical idea of the metropolis: While New York City was the only city in 1950 with more than 10 million people, it has since been outrun by several others, including Tokyo, Bombay and Sao Paolo, whose populations are nearly double that of New York today.
As people around the world flock to urban centers in hopes of maximizing the value of their labor and enterprise, so the city itself stretches to accommodate and use each new skill, muscle, womb and brain. One result is the splintering of the metropolis into many cities. Alongside the slums of the poor-who now constitute nearly one-third of urban dwellers-and the gated communities of the rich hum the cities of industry and commerce, diversion and respite. In the metastasizing Chinese megapolis of Chongquing, mountains are literally moved to make way for ersatz Tyrolean villages or French chateaux created as luxury homes for the wealthy. In the slums of Chennai, India, several families sleep packed together in shanties built over open sewers. In Lagos, markets spring up around traffic jams, gradually entrenching and turning motorways into retail districts.
Urbanism has been defined as a social rather than an architectural concept, the process by which density increases interaction between unfamiliar people, ideas and information. Yet the built environment largely determines the number and nature of those interactions. Unfortunately, many cities are growing so quickly that expansion of the built environment happens more by accident than by design. Even in older, relatively well-developed cities, economic forces such as widening income gaps, migration and the changing nature of industry are forcing huge shifts in the urban organism. To what extent are city dwellers aware of the ways in which the physical structure of their lives-the product of generations past-determines their options and choices today?
Some predict a dark, chaotic future for the world's cities due in large part to a lack of such awareness. Their pessimism is not new. The humanist Lewis Mumford believed Rome's overexpansion presaged the fate of modern megacities: "The historic outcome of such a concentration of urban power…is the last stage in the classic cycle of civilization, before its complete disruption and downfall," he wrote in 1961. Mumford believed unfettered growth would push the city off of its organic balance into a sort of bedlam, a prospect echoed in the UN's assertion that megacities will "act as city-states that are independent of national and regional mediation." Yet Mumford believed salvation lay in the city itself: By increasing exposure to the unfamiliar, it encourages creativity and innovation that can be harnessed in new solutions. This creativity can also reflect images of our cities back to us, reminding us of the need to be active in our citizenship.
Laura Peterson is a journalist based in Washington, D.C. who has lived and reported from cities including Sarajevo, Istanbul and San Francisco.