People have decided that instead of living close to the land they want to live close to each other. So we are all banding together in cities. That banding together is “The Urbanization Project”. It’s a project that started around 1800 when the World’s Urban Population was 56,000,000 and will be finished by 2100 when all the people that want to live in cities, live in cities. (Shlomo Angel, “Making Room for Urban Expansion”)

Spatial proximity may no longer be important for the delivery of material goods, but it is vital for the transfer of ideas⁽¹⁾. This is the principle on which universities, think tanks, and industrial parks are built, and it is the reason why firms in highly skilled industries tend to congregate near one another: high-tech firms in Silicon Valley, or financial firms in Manhattan or London.

Cities spur innovation not only by concentrating expertise within particular industries but also by bringing together different industries. The most important ideas come from unplanned combinations of existing ideas, and cities where such spontaneous innovations flourish will thrive.

Electronic communication can help us communicate simple ideas, and can put masses of raw information at our fingertips. However, its ability to transfer more complicated ideas—and, crucially, skills—seem still sharply constrained. Indeed, the communications revolution gives cities a whole new vitality: cities are essential to the Information Age economy.

Today half the world’s population lives in urban areas, and in the coming decades —between 2010 and 2050—cities in industrialized countries will add 170 million to their populations while developing countries will add 2.5 billion, or 15 times that. The largest shares of this growth, 25% each, will be in Sub-Saharan Africa and the Indian subcontinent, and an additional 15% will be in China.

Building more resilient and prosperous cities is perhaps the grandest of the grand challenges facing the world today but, surprisingly, city growth is taking place spontaneously in India, Africa or Latin America with no architectural master plan. There are some 4,000 cities in the world with populations of 100,000 or more. Simply studying some American or European cities and finding that they all possess a certain trait does not mean that all cities in the world have that feature. We need a better science of cities.

More than fifty years ago, thinking about the kind of problem cities pose, Jane Jacobs realized that cities happen to be problems in organized complexity, like the life sciences:

Cities, again like the life sciences, do not exhibit one problem in organized complexity, which if understood explains all. They can be analyzed into many such problems or segments which, as in the case of the life sciences, are also related with one another. The variables are many, but they are not helter-skelter; they are “interrelated into an organic whole.” (Jane Jacobs, “The Kind of Problem a City is”; Chapter 22 of “Death in Life of Great American Cities”)

She wondered: Why have cities not, long since, been identified, understood and treated as problems of organized complexity? Planners assumed that cities were problems of simplicity, but they could not avoid seeing that real cities were not so in fact. City planning, as a field, had stagnated because city planners together with businessmen, lenders, and legislators clinged to the unexamined assumptions that they were dealing with a problem in the physical sciences.

Ideas about complexity in science were brand new at Jacobs’ time and to prove her intuition would take time. A switch in thinking was necessary from ‘cities as machines’ to ‘cities as organisms’ and to have the capability to gather and process huge amounts of data related to real cities, to begin to understand the kind of problem a city is.

The recent availability of many new, large-scale data sets such as those automatically collected from mobile phone networks and massive geographical information, opens up unprecedented possibilities to systematically study the urban social dynamics and organisation. Thanks to bigger data, cities across the Globe and through time are now knowable like never before, across many of their dimensions: social, economic, infrastructural and spatial.

Today the idea that Cities are natural systems is gaining ground. Starting with a review of the conventional definition of city, we find that cities evolve spontaneously in human societies as beehives or coral reefs, and should not be thought of as arbitrary human artefacts to be redesigned at will. They are a kind of complex system, in fact, immensely complex in the many forms of information they can embody and generate.

The main empirical findings from this new body of work in geography and complex systems can be summarized in the observation that cities exist over a wide range of sizes and follow well-defined scaling laws⁽²⁾. All cities realise certain spatial economies of scale as they grow and, simultaneously, attain general socio-economic productivity gains. With each doubling of city population, on average, a city contains about 10-­‐20% less infrastructure volume per capita. It also displays a 10-­‐20% increase in rates of wealth production, innovation and, if left unchecked, of other, less benign products of human socio-economic interactions, such as violent crime.

A fundamental derivation of these scaling relations has been lacking so far. Now, in a recent paper⁽³⁾, Luís Bettencourt shows how cities may evolve following a small set of basic principles that can explain how cities change gradually from the bottom-up. He thinks that his framework provides a new unified model of urbanization, which can be used to predict the average social, spatial and infrastructural properties of cities which have been observed in nations around the world.

Bettencourt’s theoretical framework suggests that a kind of optimal city exists when we have the most social interaction – and social and economic output coming from it – with the least cost of connecting people and goods and ideas to each other. He sees the planner’s job to steer cities toward that optimal point (G* in the graph above). Beyond that point, the number of social interactions in a city can still grow, but their cost rises faster than the benefit.

C’mon, urban planners of the world! Don’t miss the opportunity: Tokyo, Mexico City, Shanghai, LA and the like are quivering with excitement waiting for your science!

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(1) Edward L. Glaeser, “Why Economists Still Like Cities”, City Journal, March 1996
(2) Michael Batty, “The size, scale, and shape of cities”, Science 319, 769-771; Feb. 2008
(3) Luís M. A. Bettencourt, “The Origins of Scaling in Cities” Science 340, 1438-1441; June 2013

Featured Image: Michael Batty, “Cities as Complex Systems”; Greater London: The evolution of the road network over the last 500 years from the centre outwards