Two SFI researchers write in the October 21 issue of Nature – a special issue on cities – that a “grand unified theory of sustainability,” with cities and urbanization at its core, must be created to help guide development and combat the multiple threats facing humanity today.

Although cities are engines of human creativity, wealth, and power, they also are the source of much of the world’s pollution, disease, crime, and other problems. Rapid urbanization and economic development during the last century – a continuing trend – have accelerated global problems, from climate change and environmental degradation to food, water, and energy shortages.

The Nature article, by SFI External Professor Luis Bettencourt and Distinguished Professor Geoffrey West, notes that although cities have infrastructures, economies, cultures, and social institutions that are deeply interrelated and dynamic, their parts often are thought about singularly. “This frequently results in ineffective policy and often leads to unfortunate and sometimes disastrous unintended consequences,” they write.

Despite their complexities, cities share remarkable, quantifiable features that lend themselves to scientific and mathematical analysis. Recent studies of large data sets show that many measurable city characteristics increase nonlinearly with a city’s size, trends Bettencourt, West, and their colleagues have shown can be expressed as simple mathematical laws. Wages, GDP, patents, and educational centers, for example, all increase with population by about 15 percent more than the expected linear growth. Crime, traffic congestion, and incidences of disease follow the same 15 percent rule.

“Our work shows that, despite appearances, cities are approximately scaled versions of one another,” the authors write.

Cities bear some similarity with other complex biological systems that are sustained by resource distribution networks, such as the circulatory or vascular systems. But, Bettencourt says, there also are fundamental differences that make cities uniquely human: social interactions and the concentration of economic and cultural activities in larger cities lead to an acceleration of time – and greater rates of innovation.

"Our work suggests that these infrastructural and social aspects of cities are intimately connected and must be understood together," Bettencourt says.

Bettencourt and West argue that a science of cities can benefit society in a number of ways. Identifying cities that deviate from scaling laws, for example, might pinpoint under- or over-performing cities and, perhaps, offer suggestions to policy makers for improving a city’s performance – or making it more sustainable – as it grows. 

Bettencourt is an SFI External Professor and a scientist in the Theoretical Division at Los Alamos National Laboratory. West is an SFI Distinguished Professor and Past President and a senior fellow at Los Alamos National Laboratory.

Read the Nature article

See Nature’s special issue on science and cities

Listen to a radio interview with Bettencourt and West

Read Radio Free Europe article

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