Urban inequality scaling – Research indicates correlation between population size and elite wealth in urban spaces

For as long as people have built cities, they have been centers of both opportunity and inequality. In ancient times, this was evident in the size of houses, the grandeur of monuments, and the inscriptions celebrating rulers and elites. Today, we see it in luxury high-rises next to struggling neighborhoods and tent cities in the shadows of monumental public buildings.

The presence of inequality in urban spaces throughout time and across cultures raises an important question: is urban inequality coincidentally common or is it something deeper---an inevitable part of how cities function? A new study led by researchers from the Max Planck Institute of Geoanthropology (MPI-GEA) set out to answer this question, finding striking quantitative similarities between ancient and modern cities when it comes to how elite wealth is expressed in urban spaces.

The researchers found that the same scaling relationships that appear to shape modern economic activity – in which cities grow richer and more productive as they get larger – may also shape the way wealth is concentrated at the top. In other words, the processes that make cities wealthy may also often make them unequal.

“Our research suggests that inequality isn’t just something unfortunate that commonly happens in cities,” says lead author Christopher Carleton, “it’s something that may grow with them, following predictable scaling patterns. It seems as if inequality isn’t a side-effect of city living under particular cultural or economic conditions; it may be a built-in consequence of urban growth itself.”

To reach these results, scientists analyzed evidence from both ancient Roman and modern cities to see how wealth – particularly elite wealth – scales with city size. The data for Roman cities included numbers of monuments and counts of inscriptions dedicating monuments to elite patrons. Data for modern cities included counts of very tall buildings, skyscrapers like the Burj Khalifa or Trump Tower, as well as counts of billionaires per city. They then applied statistical scaling methods to test for mathematical relationships between city size and indicators of elite wealth.

Results show that, as cities grow, elite wealth increases in a sublinear way, meaning that while expressions of elite wealth increase with population size, the growth in elite wealth faces diminishing returns with each increase in city size. This process results in slightly fewer increases in elite wealth indicators than the previous increase in city size produced, indicating that the rate of elite wealth accumulation slows as cities continue to grow.

Altogether, the study suggests that addressing the problem of inequality may be more complex than changing the tax code or adjusting existing policy. To confront the compounding challenges of the Anthropocene, researchers at MPI-GEA continue to seek insights from the past and apply them to modern pressing questions. As co-author Patrick Roberts puts it, “Do different types of urban planning lead to different expressions of inequality? Are there historical examples where inequality was mitigated while cities continued to thrive and increase overall wealth?” Answering these questions will help scientists and policy makers move beyond recognizing patterns to developing meaningful interventions.