Regardless of where you live or work or who you’re friends with, you usually move around the same neighbourhoods and streets of your city. It may be London, Santiago, Shanghai, or Moscow, but in any of these places, there are always districts you have never set a foot in. Have you ever considered how many ‘cities’ are within your own city?
A research article published in The Royal Society Open Science and signed by Chilean researchers utilizes big data to analyze and visualize urban segregation, delivering spatial tools that allow us to develop strategies in a city of many cities. "We know there are [social] bubbles in Santiago, Chile, and that therefore, there is segregation," says Teodoro Dannemann, co-author of the research paper The time geography of segregation during working hours, in a conversation with ArchDaily. “We know that each person explores only a small fraction of the city, which is basically the home-work trajectory. This implies that we only engage with a small group of citizens," he adds.
This research is one of the outcomes of an investigation led by Dannemann alongside Boris Sotomayor-Gómez and Horacio Samaniego, which was backed by the Eigencities project of the Econinformatics Laboratory of the Universidad Austral in Valdivia, Chile. Sponsored by Telefonica I +D Chile, the researchers worked with an anonymous X/CDR database (Call Detail Records, the data record produced by a telephone exchange) based in Santiago during working hours. The idea was to understand through smartphone data how we travel across the city.
Every time you connect to the Internet or call someone, your smartphone plugs into the nearest available antenna, allowing X/CDR databases to anonymously access your personal record of checked-in places. The researchers worked with a 350,000-user database in Santiago, where each registered track allowed them to create a movement network. The sum of these movements indicates a community.
"Each community arises from a series of detection algorithms that find the best way to divide the overall call network. This is how the social bubbles created by each citizen's trajectories are recognized," Dannemann explains.
Dannemann, Sotomayor-Gómez, and Samaniego have estimated the chances that a person who lives in any of these already identified communities will interact with someone from the same community at the workplace. When low mixing rates are detected, determined through comparison to expected outcomes in random scenarios, the researchers deduce urban segregation patterns.
The six communities identified by the researchers have been visualized in the featured image of this article — one of the most revealing and striking outcomes of their academic research. Both the communities and main avenues of the Chilean capital city are easily recognized: the metropolitan-scale Pajaritos-Alameda-Providencia Avenue (green, white, purple), the Panamerican Highway (red), Vicuña Mackenna Avenue (orange), Gran Avenida and Santa Rosa Avenues (pink), Melipilla Road (green), and Americo Vespucio Ring Road (green, pink, orange, blue).
The research team concludes that the investigation "corroborates the strong level of segregation in Santiago described by sociological literature" and confirms segregation patterns described in large Latin American cities. In the upper-class district — the northeast — the probability of meeting a co-worker belonging to the same community —or 'bubble'— reaches 44%, while in random scenarios it reaches only 20%. The most striking case in Santiago is the orange community — La Florida and Puente Alto, two of the three most populous comunas of the country — where the rate reaches 50%. According to the authors, the only exception to these trends in Santiago is the downtown area— white—, the only one that "is not statistically segregated."
The authors suggest that what is understood as movement, namely mobility, and urban infrastructure, is a key factor for stimulating interactions between citizens of the same city, and thus, decreasing urban segregation. "We want the people and their dynamics to become the focus of [urban] planning, instead of static, obsolete indicators", Dannemann says.