But cities also represent our best hope for finding solutions to these enormous challenges since they are the cauldrons of innovation, ideas and wealth creation. Thus, an urgent challenge of the 21st century is to understand cities, and by extension megacities – those urban areas with populations exceeding 15 million. 

Looking back over 150 years to megacities of the past, such as London or New York, we recognise that they suffered from much the same negative image often associated with megacities of today. Think of the Dickensian image of London: a city pervaded by crime, pollution, disease and destitution. Nevertheless, these cities were highly mobile, evolving and diverse societies, offering huge opportunities ultimately resulting in their modern manifestation as drivers of the world’s economy. Much the same could be speculated about megacities emerging today in Africa, Asia and other parts of the world. 

Recently, my colleagues and I have been developing a ‘Science of Cities’ to understand quantitatively how their socio-economic and infrastructural dynamics and organisation work. We found some surprising results. By analysing data representing a broad spectrum of urban metrics of cities across the world, we found that they all scale in a remarkably similar fashion. This means that if you know the population of a city within some urban system anywhere in the world, you can predict with 80–90% accuracy its average income, number of AIDS cases, patents, crime rate, petrol stations, length of roads, etc. So, despite history, geography and culture, there are extraordinary systematic regularities and constraints that transcend the individuality of cities.

Why is this? We believe these ‘laws’ reflect the commonality and similarity of people and social networks the world over: the connection is us. All cities share the same effective ‘DNA’ because they’re made up of people; cities are fundamentally social networks, complex adaptive systems that behave similarly regardless of geography, political system or economic model. 

How does this extend to megacities? The Survey on the Global Agenda showed that across the globe people recognise their importance, but the jury is out on their future. Will they continue to grow indefinitely without significant improvement of social conditions, or will they follow the trajectories of London and New York and develop into major economic engines and modern metropolises? Cities take decades to change, but as we look around the world there are lessons that underscore the importance of really understanding what makes them tick.

All cities share the same effective ‘DNA’ because they’re made up of people; cities are fundamentally social networks, complex adaptive systems that behave similarly regardless of geography, political system or economic model.

China, for example, has embarked on the daunting task of constructing new cities to urbanise 250 million rural residents. Perhaps out of expediency, these cities are being built without deep understanding of the complexity of cities and its connection to socio-economic success. Indeed, we are told that many of these new cities, like classic suburbs, are soulless ghost towns with little sense of community. Cities have an organic quality; they evolve and physically grow out of interactions between people. The great metropolises of the world facilitate human interaction, creating that indefinable buzz and soul of the city; the wellspring of its innovation and excitement that is a major contributor to its resilience and success, economically and socially.

In the US, Detroit shows us how neglecting diversity can lead to losing that buzz. Detroit was narrowly focused on the automobile industry, which indeed spun off other associated but highly dependent industries, which led to a temporary boom. But because of its lack of business diversity, the city was unable to adapt when the ageing automobile industry hit tough times. Cities are quintessential complex adaptive systems constrained by underlying social and infrastructural networks. Diversity is crucial for their resilience, because all of their benefits, successes and problems are thereby highly coupled, interacting and continually changing.