How public transportation predicts social media connections in New York City

 
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August 15, 2019

There’s a phenomenon economists call “agglomeration economies,” where a collection of companies become more efficient by being close to one another. The idea holds for people, too. When people cluster in dense places like cities, they share insights and resources. Strong social connections make for good economics.

A recent working paper from the National Bureau of Economic Research adds a twist to the economics of proximity: mass transit connections may be tied to social media connections, which can also spur economic success. In New York City, travel time and cost more strongly predict social media connectedness between zip codes than geographical distance, the paper finds.

How transit connections relate to social connections

“Social connections are hugely important from an economic perspective, since they allow for the exchange of ideas and information, and therefore contribute to innovation and social progress,” explained one of the paper’s co-authors, Theresa Kuchler, assistant professor of finance at New York University, via email.

The New York City region is matchless in America for the breadth of its public transportation system, which provides some 2.6 billion trips per year on subways, buses, commuter rails, through bridges and tunnels, and across “the most modern aerial tramway in the world.”

The authors start their analysis with anonymous Facebook data from March 2018 from users who had turned on location tracking. They drill down to zip codes and combine information on Facebook friendships with geographic data from the Census Bureau and city transit maps.

The results “suggest that public transportation infrastructure plays a more important role in the formation of social networks in urban settings than simple geographic distance does,” the authors write.

The longer it takes to travel between locations, the fewer social friendships there are among people in those neighborhoods. The authors find that each 10% increase in public transit time is associated with 14.2% lower social connectedness between zip codes. Meanwhile, a 10% increase in geographic distance is associated with only 8.7% lower social connectedness.

“We were surprised by just how much transit time mattered for social connectedness relative to other factors,” Kuchler explains. “We expected there to be some effect, but were really surprised by how large that effect ended up being.”

New York City has a large transit system, but that doesn’t mean places that are geographically close are easy to move between. Take the East Village in Manhattan and Greenpoint in north Brooklyn. Those neighborhoods are separated by about 1.5 miles across the East River, as the crow flies. But because there are no direct transit connections — there’s no straight-shot tunnel under the river — travel time from the East Village to Greenpoint is among the longest compared with similarly distant trips, according to the paper.

Just hail a cab?

New York City yellow taxis are iconic as the Statue of Liberty, the Yankees and thin-crust pizza, but getting between neighborhoods without efficient transit connections isn’t always as easy as hopping in a cab — especially when cost is factored in. A subway trip that can take a rider dozens of miles underground is $2.75. The base rate for a taxi ride is $2.50, but the final cost depends on distance and traffic. The average yellow cab ride is around $13, according to one study from 2016.

The more a cab ride costs between neighborhoods, the less social connectedness those neighborhoods have. Each 10% increase in cab cost was associated with a 10.6% decline in social connectedness, the authors of the working paper find. (They didn’t analyze transportation network companies like Uber and Lyft.)

Transit links ‘shrink’ geographic distance

Little Neck and Oakland Gardens are next-door neighborhoods in the borough of Queens with very different transit connections to midtown Manhattan — and very different patterns of social connectedness. Little Neck has two stops on the Long Island Railroad, which goes into midtown, while Oakland Gardens has no stops.

Likewise, Oakland Gardens isn’t very socially connected to any zip codes in Manhattan. But for Little Neck, zip codes in midtown and nearby Manhattan neighborhoods are as socially connected as some closer zip codes in Queens. Transit links, it appears, can “shrink” geographic distances, according to the authors.

“Obviously this does not by itself prove that it is the transit access causing the connections, but it is a case study that is highly consistent with everything else we find in the paper,” Kuchler explains.

‘A diverse set of friends’

Neighborhoods where people have a higher percentage of Facebook friends more than 5 miles from them have some of the highest incomes and education levels out of the 182 New York City zip codes studied.

Kuchler cautions that this is not a causal relationship but nonetheless is “highly consistent with a large prior literature suggesting that exposure to diverse ideas and information is central for your economic outcomes.”

The authors also look at socioeconomic factors beyond cab costs that can affect social connectedness. Areas of the city with similar education levels and racial makeups are more likely to be socially connected. And distance has less of an effect on social connectedness across neighborhoods that are both wealthy or both poorer. But travel time retains the strongest overall association with social connectedness, the authors find.

“What our work shows is that public transit infrastructure is central to allowing people to connect with a diverse set of friends within the city, and to therefore benefit from the exchange of ideas and information,” according to Kuchler.

 

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Citation: Bailey, Michael; Farrell, Patrick; Kuchler, Theresa; Stroebel, Johannes. “Social Connectedness in Urban Areas,” National Bureau of Economic Research, July 2019, Working Paper No. 26029.