Recently there have been several reports about people moving out of cities and into the countryside. This apparent urban exodus, prompted in part by the mass move to online working, raises two questions: What are cities for? And can their function be replicated by people working and living remotely?
Researchers from a wide range of backgrounds have established that cities fulfil multiple roles. But one theme that consistently appears is their role in generating social interactions.
In short, cities provide an environment for people and ideas to come together. And the bigger the city, the more interactions they create.
As the graph below illustrates, this is because the number of links between individual members of a group scales exponentially as group size increases. And the same dynamic plays out on a larger scale in urban environments: as a city’s population grows, the number of possible social interactions within its walls rapidly increases.
From the chaotic randomness of these social encounters emerges a surprisingly ordered set of outputs. For it is not just the number of social interactions that increases exponentially as urban populations grow: income, wealth, and innovation (as measured by patent production) all do exactly the same. And, up to a limit, so does average pedestrian walking speed.
Remarkably, these socioeconomic phenomena all scale predictably with an exponent of around 1.15. In other words, when a city population doubles (or grows by 100%) these quantities typically increase by around 115%.
This is called superlinear scaling, and is simply a product of the increase in individual social interactions – an increase that is difficult to reproduce in an online environment, as anyone who has experienced a populous video call will know.
At the same time, the energy and infrastructure requirements of a growing urban population also scale exponentially. But in contrast to the above, the exponent for quantities such as the length of roads, water pipes, and electrical lines is around 0.85.
This is known as sublinear scaling, and means that each doubling of population size results in a systematic efficiency saving of 15% – so as cities grow, they do more with less.
These patterns appear predictably within almost every country from Chile to China – a phenomenon known as the ‘universality of urban scaling’. In practice, this means that if someone tells you the population of a certain city, by looking at other cities within the same country you can predict quantities such as the number of petrol stations and patents produced with around 85% accuracy.
These findings explain one of the most important functions of cities: they create serendipitous social interactions and reliably convert them into new ideas, opportunities, and possibilities.
In addition, this research explains why the countryside grass may have looked greener to city-dwellers during the pandemic. Starved of its vital ingredient of social interaction, the city’s capacity to generate valuable social and economic output is severely inhibited.
All of this suggests that once lockdowns are lifted, cities are unlikely to be dethroned by the collective shift to remote working. For all the merits of video conferencing and other social technologies, in their current form they struggle to generate the chance combinations of people and ideas upon which human creativity and invention so often depend.
For now at least, you need a city for that.
