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Life in the Fast Line

As cities grow, the pace picks up

No two cities stand alike. With skylines that stagger in an infinite number of ways, each city has its monuments, its landmarks, its grid of roads and its masses of people and cultures that make it different from any other metropolis in the world. Underneath the obvious, however, a recent study says cities are more similar than what meets the eye. While urban dwellers tend to claim their city is like no other, Chicago is more akin to Shanghai, Berlin and Los Angeles than a spectator would guess.

"We're interested in measuring in what sense can one talk of cities being similar to each other," says Luis Bettencourt, co-author of the April report in Proceedings of the National Academy of Sciences USA. "This is a question that's been around for a long time, at least since classical times. Aristotle wrote about it. People tend to look at cities visually or now through satellite photos, at the shapes of cities, and by those measures, cities are very different and develop differently. But what's interesting is that in terms of rhythms of human behavior, socioeconomic and other social activities, cities are similar objects that get sped up as the city gets larger. It's a social dynamic that's very universal."

Bettencourt is a research scientist in Los Alamos National Laboratory's Theoretical Division. He and his colleagues measured how similar cities are by using scaling laws--placing how we live in a mathematical context. Geoffrey West, renowned for his work with universal scaling laws and president of the Santa Fe Institute, is one of the five authors, who also include researchers from Arizona State University and Dresden University of Technology in Germany. The authors explored how different indicators of cities' activity and infrastructure scale with population. Beginning their research two and a half years ago, they studied cities across the United States, including Chicago, along with cities in China and Germany. For almost as long as cities have existed, they've been compared to biological organisms, which is where the researchers began their study.

"We started looking at measures of energy consumption because we wanted to basically assess that against what happens, for example, in biological organisms," says Bettencourt. "The sociology school in the United States is the Chicago School, and they had a very strong sense in the beginning that as Chicago developed and was growing so fast they were seeing the transformations--some of them had to do with the diversification of economic activities, but also people had to live with different people, not necessarily people they would have grown up with and the speeding up of life--so they had speculated that this was an ecology or an organism. They had discussed qualitatively many things that we now measure. So it's very interesting to have that background and to able to quantify some of these factors.

"With an organism, what happens is that there's sort of an interesting analogy," Bettencourt continues. "In an organism, you have the heart, lungs and these places where energy is pumped from, and then they have to reach every part of the organism. That just happens through these networks that condition the flow of those resources, and then the cells at the end have to work at the pace at which they get resources. So that was the hypothesis--maybe cities can be a little bit like that."

The researchers studied the cities according to three types of factors: human needs (energy consumption and housing), material infrastructure (electrical cables and road surfaces) and patterns of social activity (like patents, bank deposits and new cases of AIDS). What they found was interesting. Harvard Business Review called it one of the "Breakthrough Ideas of 2007." Quantities accounting for infrastructure were economies of scale, while those reflecting wealth creation and innovation had the same scaling exponent, showing increasing returns. What this meant was the larger the city, the more human interaction and the more innovation and wealth creation. The pace of the city continually gets faster as it grows, and the demands to keep up with the acceleration increase. This is very different from what happens in biological organisms--the larger those organisms get, the more they slow down. Bettencourt says this was a fact economists knew about, but they hadn't interpreted it in terms of the similarity law between cities and hadn't seen it as a rhythm.

"All these social quantities, what's interesting about them are their paces, their rhythms," Bettencourt says. "It's wages per year, crimes per year, patents per year, the pace at which somebody walks. All these things are something that's happening in a time. What a city seems to realize is that by intensifying the number of interactions that people have in a smaller space, it creates this acceleration of social life that leads to all the things we do socially, both the good and bad--wealth creation and innovation, but also cost, congestion, crime, disease, etc. Part of our contribution is to quantify this, to show the general phenomenon that happens not just in one country, but across cultures and time."

It's difficult to imagine wealthy and modern cities like New York being, at their root, the same as industrializing cities in China. Bettencourt says what separates them are their baselines. People on average in Shanghai makes less per capita than people in U.S. cities, but the similarities between cities of different sizes in China and the United States, measured by the exponent beta, is the same.

"Certainly different cities in the United States are very different in the economic activity that they've had traditionally," says Bettencourt. "Chicago has its history. New York has a different history. Los Angeles is very different. That's the source of how wealth was made or innovation. People in Europe who were thinking about the same problems would say that in Europe the economy is different, so why should this be true? But the effect doesn't seem to depend on what is done economically. Large cities tend to integrate more economic activity in a way that we're now measuring, so they're more diverse, but the gain in productivity is the same regardless. We were surprised that the similarities were so predictive of economic activity--spectacularly predictive."

In the study, the authors found that "as population grows, major innovation cycles must be generated at a continually accelerating rate to sustain growth and avoid stagnation or collapse."

"The nature of bringing people together is that you start creating change, both good and bad, at a faster and faster rate," Bettencourt says. "It seems that the natural mechanisms that lead to growth have to do with innovation and wealth creation, and these typically accelerate the rate of growth. But at some point that's not sustainable, and you have to have a major adaptation. You either need to build new roads or new mass transit or you need to slow down people coming in by some way. In the history of the United States, some of these are natural and normal, like the Civil War was a big effect or changes in policy on immigration. At some point, if nothing gets done, the city enters a crisis. Costs get too high, and congestion becomes unbearable. We've seen that since ancient times. That can actually lead to population decrease, so the best thing is to try to avoid that by having a means to take a breather, so to speak."

Bettencourt calls the relationship between a city's good (wealth creation and innovation) and bad (cost, congestion, pollution and crime) "a very dynamical balance." When the bad takes over, people start leaving, which was what happened to New York in the late 1960s and early '70s, after the city's greatest ever absolute increase in population.

"So there are these feedback effects," Bettencourt says. "Too much growth is not good. That's the place where city authorities can make a big difference. It's very important to keep that balance in check."

Cities also teeter in a precarious position when they become too specialized, which was what happened to Detroit, a place that Bettencourt says, due to a significant number of new patents filed, "doesn't look so terrible now." Cities along the U.S. Rust Belt became too specialized, along with English cities like Manchester, which creates decreasing returns to scale. The more diverse a city is, the more ready it is to adapt.

"The idea is that you can only exploit what you have so long," Bettencourt says. "That was the model for what should happen to a city, and in fact, it is the current model for what people think happens to many businesses. A business is more specialized than a city is. In the business community, it's thought that larger size means you slow down. But in cities by and large, that's not true."

Many of today's fastest growing cities are sprawling urban landscapes, like Phoenix and Las Vegas. People seem to be moving from more expensive cities to places where land is more readily available and reasonable.

"Cities can grow faster if it's cheap to grow," says Bettencourt. "This seems to happen with sprawling cities. What's interesting, though, is this doesn't seem to effect the fact that they still follow the scaling laws. It's interesting to think whether these cities will become interesting, compared to San Francisco, Chicago or New York. Will they develop the innovation, the wealth creation, the interesting aspects of bigger cities?"

Bettencourt, a self-professed lover of cities, says he just likes "to see what happens when you put a lot of people together." He recently returned from Tokyo, which he says he finds fascinating. "The fact you can have such a large city with no crime, with complete security and totally clean shows that it's possible to have people living like that."

The authors hope this study will lead to other city and scaling studies, likely incorporating rapidly growing cities in developing countries, and will help cities around the world maintain a balance.

"For us, this was very interesting to realize that cities are so different in the way they look, the way the people live, the language they speak, what they eat," says Bettencourt, "but there's this universality to the human dynamic, the way we come together. From an academic point of view, that was very satisfying."

Published: May 28, 2007
Issue: Summer 2007 Urban Living