Looking at Yves Marchand and Romain Meffre’s recent photoessay on Detroit, one can’t help but wonder what happened. How did a city that was literally the engine of the American economy sputter and decay into a mass of peeling paint, broken windows, and faded twentieth-century glamour? And on the flip side, how can a city like Dubai, with its Burj Khalifa tower stretching nearly 1 km into the sky, rise out of the desert in such a short period of time?

These are some of the questions that Chris Kennedy’s new book, The Evolution of Great World Cities, seeks to answer. Kennedy is a professor of civil engineering at the University of Toronto with a soft spot for cities and economics. Launching the book in London last week, he noted that he originally wanted to investigate the wealth of cities in much the same way that Adam Smith had done for the wealth of nations. But along the way, the book changed into something subtly different and the result is a fascinating mix of macroeconomics, infrastructure engineering, history, and ecology.

The book has three main themes. First, it provides a useful definition for the wealth of cities, namely as the cumulative assets of its citizens. This omits the value of public buildings and infrastructure, a distinction that seems counter-intuitive at first. How can a city’s most prominent buildings, such as Philadelphia’s $6 billion dollar town hall not be included in such a total? However as Kennedy describes, the value of these facilities is reflected in the locational value of people’s homes; a home with access to first-rate transport, water, and energy supplies will have a higher value than a cabin in the woods with no such services and amenities. Using the example of 16th century Seville, the importance of citizen ownership is also demonstrated. Tonnes of Incan gold may have flowed through Seville’s gates, but most of it was destined for the hands of foreign owners, namely the bankers in Antwerp and Genoa that financed many of the trans-Atlantic expeditions.

The second theme is the connection between economic growth and the physical structure of cities. Take the automobile as an example. Its introduction in the early twentieth century led to a new mode of urban development, suburban sprawl, which although it has many disadvantages certainly leads to increased consumption. Cars need to manufactured, sold, and serviced; larger suburban homes need to be constructed with more materials and filled with consumer goods. The key issue here is not the infrastructure itself, but the modes of consumption that it necessitates. For example, one might expect that the 1990s IT revolution would have led to a demand side crisis. Just like Smith’s pin-makers, those displaced by the productivity gains of IT – bank tellers, backroom operations, and so on – would be unemployed and unable to consume. However IT also created new opportunities in PC manufacturing, software design, and innovative business models like EBay and Amazon. This new online way of life drove a new cycle of demand, rejuvenating the economy.

To me, this is the book’s most important contribution. This idea of the autonomous consumption of infrastructure, that is the societally mandatory level of minimum consumption created by these systems, is hugely important for understanding not just the economic growth that Kennedy is concerned about, but more broadly the sustainability of cities. North American urban sprawl is a perfect example. While it engenders high levels of consumption, maintaining that lifestyle depends on a throughput of resources, most importantly abundant and affordable transport fuel. Should these fuels become significantly more expensive, these cities would grind to a halt. The same level of infrastructure-mandated autonomous consumption would still be there, but it would now consume a much larger portion of a household’s income, leading to reduced savings, reduced investment in new opportunities, and eventual stagnation. In the language of sustainable development, the autonomous consumption of infrastructure represents a liability that must be serviced on an on-going basis.

The third theme is an analysis of urban economic processes as ecological systems. The relevant chapter offers several noteworthy ideas but it felt incomplete compared to the rest of the tightly-argued book. Nevertheless, an excellent description of Detroit’s decline is provided and the statistics cannot fail to astound: a population decline of 50% between 1930 and today, over 60 square miles of vacant abandoned land (44% of the city’s area), local tree species poking through factory floors that once produced millions of automobiles. Kennedy argues that, in much the same way that an ecosystem needs diversity to survive a changing environment, Detroit was too focused on cars in order to survive, both in terms of the limited diversity of its economy and the inflexibility of its infrastructure. One of the great what-ifs posed by the book is what Detroit might look like now had a 1923 proposal for a subway and integrated transit system been implemented.

Illustrated with case studies on cities as diverse as Toronto and Montreal, Philadelphia and New York, Seville, Paris, Dubai, and London, The Evolution of Great World Cities is a unique work of economic geography. Engineers often complain that economic models are too abstract to offer a meaningful understanding of the real world. Kennedy has therefore done both professions a great service by presenting a strong argument that it is the links between our built environment and economies that matter most.

Chris Kennedy has also written a blog post about the book over at the World Bank’s Sustainable Cities site.