October 19, 2021

I, Science

The science magazine of Imperial College

How would you describe a city? A unique maze of people-lined streets? A series of districts linked through things which make up your life; that coffee shop you like, that bar that serves the best margarita, and home? However you describe it, you probably don’t think there’s anything similar, or even scientific, linking all the cities around the world.

But Geoffrey West, a physicist captivated by finding mathematical answers to fundamental questions, was enticed by the seemingly random and complex collection of cities around the world. He sought for the mathematical rules that govern urban areas.

Before cities, West had taken on biology. He searched for the equations that would explain every aspect of life. He claims that, given the size of an animal, he is able to tell you every single one of its characteristics, such as the pressure on the wall of the third branch of its artery. Although controversial, his arguments are compelling.

When he turned his attention to cities, he asked some unusual questions, “Maybe London is just a great big whale? To what extent is a city an organism?” This isn’t a trivial subject, by 2030 it is estimated about around 4 billion people will live in urban areas. It is important that we can understand the secret rules that govern our lives in these areas, but the seemingly endless variations in cities all over the world couldn’t surely be connected by a universal set of rules. How could historic London compare to the geographically-isolated New York?

West and his colleagues accumulated a mind-boggling wealth of numbers and statistics pulled from the dullest databases imaginable. From this seemingly never-ending data set, they started to create information and the reveal the secret science of how we live in a city.

After two years worth of analysis, the team presented a handful of elegant equations describing a whole host of urban variables. A city became an organism in their eyes, and to their delight each of these organisms were the same, just on different scales. If given the population figures, the equations they produced allow them to predict a diverse range of factors for a city with 85% accuracy. These factors are as detailed as the average income of the city’s dwellers, and even the dimensions of its sewer system.

His first observation was that, as with a biological organism, the infrastructure of a city was scaled sublinearly. But what was more interesting was the range of indicators that had a social element to them. According to the data outlining economic factors, whenever a city doubles its population, the economic activity increases 15% per capita. In simple terms, a person living in a bigger city does more of everything. This was even observed for the negative variables; double the population and 15% more crime is experienced per person.

West had in fact initially predicted the exact opposite. The fact that all these diverse factors scale in a very similar manner, even in different cultures on different continents, suggests that a human social dynamic drives them all. West emphasised that cities are valuable human dwellings as more social interaction is facilitated through proximity; ease of access to people determines views and disciplines, as well as chance meetings.

Cities are an important human invention; they allow us to be more productive than our physiology truly allows. But, however unique our lives and our cities may seem, West has shown that we live by an unseen code. We all live by a simple set of equations which dictate how our bodies work and the way we live with each other.