Cityscape (Image: Pete Linforth/Pixabay)

Traffic regulations, liquor licensing, residential zoning — these are examples that might come to mind when we speak of city laws. Yet these are not the only laws that govern cities.  SFI Professors Chris Kempes and Geoffrey West (Distinguished Shannan Professor of Complex Systems) have tapped into a very different set of laws that pertain to urban life. If we understand these latter laws, Kempes and West argue in their op-ed at The Bridge, they can help us navigate the pitfalls of our rapidly urbanizing world — including planning for pandemics like COVID-19.

On the one hand, the growth of cities is a boon: they foster synergistic wealth creation, information sharing, and creativity. So, too, however, do they leave behind more entropic phenomena: increases in crime, disease, pollution, and systemic inequality. Can we reap the benefits of urban centers without suffering the entropy they exhale? Yes, Kempes and West argue, if we understand better the more universal laws that govern them.

Kempes and West have discovered two such laws. The first pertains to how cities consume energy: in cities, energy per capita, (measured in terms of infrastructure — gas stations, roads, electrical lines), decreases in proportion with city population size, on average, with an exponent of about 0.15. A similar law appears in the biological world: “the energy required to support a unit mass of tissue decreases systematically as the quarter-power of body mass.” Both cities and organisms in this sense produce economies of scale: as they increase in size, they use resources more efficiently.

Yet cities exhibit another scaling law that looks very different from the biological world. The increased connectivity of cities, Kempes and West explain, gives rise to a “super-linear scaling of socio-economic activities.” As cities increase in size, so too do per capita wages, patent production, and GDP, along with crime, inequality, and disease — all at a universal rate, raised, on average, to an exponent of 1.15.

How can these scaling laws help us? For Kempes and West, they are the beginning of a science of urban life. We might think that cities get their most significant qualities from their particular history or geography, but all cities exhibit law-like universal patterns in relation to their size. When we see these kinds of universal scaling patterns clearly, we can begin to optimize the strengths of cities while mitigating the social entropy they generate in times of crisis.

Read the article, "The Simplicity and Complexity of Cities," in The Bridge (December 17, 2020)

Download the full issue for additional contributions by SFI Science Board members Susan F. Fitzpatrick (James S. McDonnell Foundation) and Simon A. Levin (Princeton), and External Professor Rajiv Sethi (Barnard College, Columbia University) and Brendan O'Flaherty

Read a related SFI Transmission essay, "T-025: Chris Kempes and Geoffrey West on understanding cities to respond to pandemics" (May 4, 2020)