Nat. Hum. Behav. https://doi.org/djtz (2020)

A graduate with a specific expertise, such as flow cytometry, could move to a city, where they will likely find more job opportunities in, say, biotechnology labs. While this choice might appear obvious, the reasons for the disproportionate concentration of economic activity in urban centres are less clear. Pierre-Alexandre Balland and colleagues have now found that such spatial concentration increases with the complexity of activities.

An activity is considered complex when it requires a large team of highly-skilled experts with complementary expertise. The authors analysed data on patents, occupations and industries in the United States; they used proxies for knowledge complexity — such as the size of a team responsible for a patent — and found that spatial concentration increased with the number of inventors. The connection between economic activity complexity and urban concentration could explain the spatial inequality between small and large cities.