Where Do People Meet? Urban Segregation in Cellular Data

Ott Toomet, Siiri Silm, Rein Ahas, Erki Saluveer, Tiit Tammaru

Immigrants and ethnic minorities often live more or less separately from the majority population. This fact is sometimes touted as a major problem that hampers social integration. But does the place where we live actually matter? Anecdotal evidence suggests that we do not interact much with our neighbors. Why should we worry then who they are?

To shed more light on this issue we analyzed the spatial behavior of Estonian speaking and Russian speaking population in Tallinn, Estonia. It is an interesting city as it is almost 50-50 split between the corresponding ethnic groups. We used cellphone data for the analysis. Mobile operators always record which antenna talks to our phones, and such data essentially form a spatial track of our activities where one can see our approximate location and time. It is relatively straightforward to analyze the tracks and deduce who were close to each other, and when and where it happened. Looking at the repeated patterns of calls we can also guess where people live and work. In this way we can see who can potentially meet each other, and where such meetings might occur.

So, are Estonian speakers close to Russian speakers in Tallinn? Well, it depends on when. We find that when at home and at work, both groups are substantially segregated. However, this is much less true when people are elsewhere and busy with other tasks, such as shopping, but also during various leisure-time activities. Even more, such free-time segregation is not closely related to the environment in the place of residence and place of work (see the figures). Even those who live in almost completely Estonian or Russian neighborhoods experience a rather mixed free-time environment.

Fig 1. Relationship between free-time meetings and composition of residential neighborhood. Circles and triangles represent the averages across different neighborhoods. For Russians (red triangles), the percentage of Russian speakers ranges between less than 10% to almost 80%, for Estonians (black circles) between 20% and almost 100% (horizontal axis). Despite of living in such different neighborhoods, during free-time both groups meet own-group members for approximately 50-60% of the time.

Fig 2. Relationship between free-time meetings and composition of work neighborhood. The message is similar to that in Figure 1: work neighborhoods vary a lot, but it is not closely associated with our free-time environment.

What do these results tell us? There are several interesting conclusions.

• residential segregation may be less of a concern than often suggested. We spend much of our active time elsewhere, and much of the time we are at home we sleep.
• As a typical European city, Tallinn has a dense urban core where a substantial part of these meeting occur. It suggests that a dense vibrant downtown is favorable for bringing together people of different background. The results for Los Angeles may well be different.
• Finally, we do not know what is behind these meetings. Most of these are probably related to just being close to each other in a crowded city. But so are our relations with our neighbors: most of them we would not even recognize on street. There is need for more analysis on what are the "meaningful places" in terms of where do we actually socialize with people.

The full article is available at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126093

Tartu Eastern Beltway: How Does It Influence the Downtown?

The largest traffic project in the coming years in Tartu is possibly the Eastern Beltway, including a long bridge over Emajõgi. This should lead some traffic away from the overloaded streets in the inner city. I have never seen a discussion about the potential impact of it on the downtown and the city structure. I give a few thoughts here, mostly from pedestrian and cyclist perspective.

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The beltway improves the accessibility of outskirts, including South Mall (Lõunakeskus).

The new bridge, road, and railway underpass will facilitate the access to South Mall and other far-lying areas for the inhabitants of Annelinn, the largest residential neighborhood in Tartu. In this way the customer base in the outskirts may grow at the expense of the downtown. True, it may crowd out primarily the smaller shopping centers in Annelinn itself and the impact on downtown may be limited—it depends on where Annelinn inhabitants currently do their shopping. However, I can hardly see how the opposite could happen—the new ring road improving the competitiveness of the inner city. There is one potential case though—more customers will be attracted to the less trafficked downtown when transit moves increasingly to the beltway. As the accessibility of the outer areas improves substantially more than that of downtown, I do not expect this to happen.

In the long run, better accessibility encourages businesses and public sector institutions to locate to the outskirts. This further increases one of the main obstacles for cycling/walking in Tartu—many important institutions are too far away and hardly accessible without a car.

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Cyclists not welcome here...

The new road will slightly lessen the traffic in the central areas. However, the city will not use that opportunity by making the streets better accessible for pedestrians/cyclists.

The previous expensive traffic project—Freedom Bridge in downtown—was intended to facilitate the traffic on the other bridges. Unfortunately, there has been no major improvement for pedestrians in the related area (we can rather talk about a slight worsening because of the new street). Theoretically, part of improved accessibility for motorists might be transformed to better conditions for other modes of transportation as well. Almost none of it has happened in the downtown (two-way Lai street improves access for cyclists, but this was not the primary goal of the project). No bicycle lanes were added when the Riia-Turu junction was reconstructed, and those along Narva street are still hardly usable. The sidewalks along a number of much trafficked streets (Jakobi, Kroonuaia) are still very narrow.

I do not believe anything will be different when Eastern Beltway opens. Bicycle lanes will probably be constructed along the new road, and with some good luck these will be largely usable. However, nothing will be done in the more important central districts. There will still be a minor improvement as the traffic load in downtown will slightly fall.

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A major boost for downtown would require fast, convenient, and affordable mass transit lines that cross in downtown.

I can imagine two light rail lines -- one from Ihaste to where the Institute of Physics is currently located, and another from Ülenurme to the location of the University of Life Sciences, crossing in downtown. If these trains are fast, frequent, and affordable, they could potentially bring people from many areas (including Annelinn) into the center.
I do not expect any of this to be realized in my lifetime, but some exploratory analysis might well be worth doing.

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Eastern Beltway is a step toward making Tartu a sprawled city where efficient public transport is hardly feasible and distances are too long for cycling/walking. The municipality should consider counter moves.