Human mobility networks reveal increased segregation in large cities

"Abstract
A long-standing expectation is that large, dense and cosmopolitan areas
support socioeconomic mixing and exposure among diverse
individuals1,2,3,4,5,6. Assessing this hypothesis has been difficult
because previous measures of socioeconomic mixing have relied on static
residential housing data rather than real-life exposures among people at
work, in places of leisure and in home neighbourhoods7,8. Here we
develop a measure of exposure segregation that captures the
socioeconomic diversity of these everyday encounters. Using mobile phone
mobility data to represent 1.6 billion real-world exposures among
9.6 million people in the United States, we measure exposure segregation
across 382 metropolitan statistical areas (MSAs) and 2,829 counties. We
find that exposure segregation is 67% higher in the ten largest MSAs
than in small MSAs with fewer than 100,000 residents. This means that,
contrary to expectations, residents of large cosmopolitan areas have
less exposure to a socioeconomically diverse range of individuals.
Second, we find that the increased socioeconomic segregation in large
cities arises because they offer a greater choice of differentiated
spaces targeted to specific socioeconomic groups. Third, we find that
this segregation-increasing effect is countered when a city’s hubs (such
as shopping centres) are positioned to bridge diverse neighbourhoods and
therefore attract people of all socioeconomic statuses. Our findings
challenge a long-standing conjecture in human geography and highlight
how urban design can both prevent and facilitate encounters among
diverse individuals."
https://www.nature.com/articles/s41586-023-06757-3