People living in large cities are more segregated, and mix less with those from different socioeconomic backgrounds, than people in small towns, according to an analysis of anonymous phone data from more than 9 million people in the US.
A longstanding premise of urban design is that cities encourage interactions between different economic groups, and so lead to less segregation. One of the most common ways to measure this segregation is to look at where people live and their corresponding economic status.
Measurements like this seem , but some argue that this static snapshot is incomplete and needs to include how people move and interact when they aren鈥檛 at home.
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Now, at Stanford University in California and his colleagues have used smartphone data on 1.6 billion interactions between 9.6 million people in more than 382 US towns and cities to show that the largest cities, in fact, cause more segregation between people from different socioeconomic backgrounds.
First, Leskovec and his team looked at where each phone, representing a person, was located at around 2 am, when they were likely to be at home sleeping. 鈥淔rom this, we infer their income, their socioeconomic status, and then we look during the day, as these cell phones move around, how often these cell phones cross paths,鈥� says Leskovec.
The researchers defined crossing paths as being in a 50-square-metre area within a 5-minute period. They also experimented with more and less strict definitions, changing the space and time boundaries, but this didn鈥檛 alter the findings.
They found that their interaction-based measure of segregation was 38 per cent lower, averaged across all areas, than a static measure of segregation, indicating that previous studies may have overestimated segregation when only considering home location.
But they also found that segregation was 67 per cent higher in the 10 largest cities they looked at than in the smallest, defined as having fewer than 100,000 people. Leskovec thinks that this higher segregation is because cities have such a diversity of different places for people to go. 鈥淭his basically allows people to kind of bucket themselves into more fine-grained buckets. The more buckets you have, the more equals to yourself you can find because you slot yourself in the appropriate bucket,鈥� he says.
Leskovec and his team also found that the least-segregated locations in a city were places like museums and shopping centres that people frequently visit, and that their locations were key for the socioeconomic groups they attracted. One way of reducing segregation between people of high and low income could be to strategically place these areas between diverse neighbourhoods to act as a 鈥渂ridge鈥� between two groups, says Leskovec.
鈥淲hat is new and interesting in what they鈥檙e doing is the use of mobile phone data,鈥� says at the University of Bristol, UK. 鈥淭hat large kind of spatial data set means that they鈥檙e able to capture the population movements in a way that we haven鈥檛 been able to do before.鈥�
However, the data isn鈥檛 detailed enough to suggest whether people are truly interacting or just being in the same space, says Manley, and different data sets could be needed to get that higher level of detail.
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