Click the image below to open the full map in a new window.
The bars on this map show three types of job skills—analytic, social, and physical. (The categories have been created by the author and his colleagues, based on detailed data compiled by the U.S. Bureau of Labor Statistics on more than 800 occupations.) The height of each bar is a measure of the average mix of skill within a given city’s labor force—the higher the bar, the more advanced the skill level within that city.
Circles measure average income within each city.
The history of human progress is intimately intertwined with that of cities. The Epic of Gilgamesh—perhaps the oldest known work of literature—closes with an awed description of the walls of the city of Uruk. Plato’s Republic—which envisioned an ideal city—was a product of the cultural and intellectual flowering of the earthly city of Athens, as well as a broadside against its politics. Dante, Petrarch, Boccaccio, Brunelleschi, da Vinci, and Michelangelo all were born in or near the city of Florence. Great thinkers, artists, and entrepreneurs—what I call the creative class—rarely come out of nowhere. They cluster and thrive in places where the conversation and culture are the most stimulating.
Even deeper in our past, the congregation of populations into progressively larger, denser, and less isolated groups may have been what enabled humanity’s rise. Archaeologists and anthropologists have long noted evidence of a flowering of artistic and material creativity that occurred roughly 40,000 years ago in Europe, reflected in everything from cave paintings, figurines, and jewelry to the complex tools that allowed our ancestors to begin actively transforming nature. Some scientists attribute this leap to evolutionary advances in cognition and memory alone. But more-recent research puts communities—not genes—at the center of this evolutionary watershed.
Research by Stephen Shennan at University College London, Robert Boyd at UCLA, and others indicates that shifting demographics was an important cause of early leaps in human development. Shennan’s research—which notes that artistic and technological leaps similar to the one in Europe had occurred in Africa and the Middle East tens of thousands of years earlier—suggests that what all these leaps had in common was the growth of local population density beyond a certain threshold. (Many of these cultural blooms withered, Shennan observes, when populations subsequently shrank.) Boyd’s research shows the close relationship between toolmaking advances and population size. As people gathered into larger groups and came into contact with one another more frequently, knowledge was shared, retained, and advanced more easily. From the earliest periods of modern human history, cultural development and technological development have been closely linked to rising population density.
They still are today. One simple indication of the economic advantages held by large, dense cities is their explosive growth over the past century and more—growth that is still continuing rapidly. America’s largest cities, each of which held no more than a few hundred thousand people in the mid-19th century, surpassed 1 million by the century’s end. By the middle of the 20th century, New York City had surged past 10 million residents; today, Greater New York contains more than 20 million people.
More than half the world’s population now lives in cities and metro areas, a proportion that is projected to grow to more than 70 percent by mid-century. China’s economic development in recent decades has been propelled by the rise of its cities—130 of which are home to 1 million people or more, including Shanghai with a metro population of 19 million and Beijing with 17.5 million. The Tokyo metro area, home to more than 35 million people, produces almost $1.2 trillion in economic output each year, roughly as much as Australia.
Researchers affiliated with the Santa Fe Institute have identified the mechanism that underpins city growth and development as an accelerated rate of “urban metabolism.” Unlike biological species, whose metabolism slows as they get bigger, successful cities exhibit faster metabolism as they grow—a phenomenon that the researchers dubbed “superlinear” scaling. “By almost any measure,” they wrote, “the larger a city’s population, the greater the innovation and wealth creation per person.” There seems to be no limit, as yet, to the relationship between greater density and faster growth.
For centuries, the specific geographic advantages of cities tended to obscure their underlying social role. When agriculture powered economic development, cities grew near fertile soils. In the industrial age, access to raw materials and ports became critical, along with the presence of enough physical labor to run large factories. But as those factors become less important, we can see more clearly what has arguably mattered the most all along.
Cities are our greatest invention, not because of the scale of their infrastructure or their placement along key trade routes, but because they enable human beings to combine and recombine their talents and ideas in new ways. With their breadth of skills, dense social networks, and physical spaces for interactions, great cities and metro areas push people together and increase the kinetic energy between them.
As highly skilled people concentrate in these places, the rate of innovation accelerates, new businesses are created, and productivity—and, ultimately, pay—grows. Wages generally increase with city size, as opportunities for specialization and interaction multiply. Pay for manufacturing workers tends to rise above the national average, for instance, as communities grow beyond 120,000 people. When my colleague Charlotta Mellander and I looked at the distribution of work across U.S. cities and metros, we found that the wages for knowledge-based jobs were markedly higher than average in locations where labor markets number 1 million people or more. In other words, the critical mass for knowledge work is higher than for manufacturing: the knowledge economy thrives at a larger scale.