In her 1961 book The Death and Life of Great American Cities, the urban theorist and author Jane Jacobs wrote about what makes cities dynamic, safe, and humane. Responding to what she saw as negative trends in American urban planning (including plans to remake her native New York), she proposed that physical environments need to meet four conditions.
They needed to have: 1) mixed use neighborhoods, with residential, commercial, and industrial buildings; 2) small blocks that promote walking 3) a mix of old and new buildings that cater to high- and low-rent tenants, and 4) sufficient density to create a critical vital mass. If cities miss any one of these elements, a neighborhood could fail.
Jacobs was influential in stopping the redevelopment of Toronto and parts of New York City. But critics complained that her theories were not founded in any actual evidence: Her ideas seemed true, but you couldn't prove it. Well, now it may be possible. New research using mobile phone data as a proxy for vitality shows that the design of cities has a strong bearing on activity, and that Jacobs was largely right in calling for certain urban conditions to be met.
Marco De Nadai and Jacopo Staiano, two researchers from Italy, argue that mobile phone data is a useful and cost-effective way of tracking whether cities are vibrant. Their aim is to replicate research carried out in Seoul using in-person survey data, but to achieve the same results more cost-effectively. Whereas that attempt to "operationalize" Jacobs's ideas took 10 years, their research was completed in three months.
De Nadai and Staiano took six months of mobile phone data for six Italian cities—Rome, Naples, Florence, Bologna, Milan, and Palermo—tracing the location of mobile links to the internet on city maps. Then, as a proxy for urban diversity (say, the land use mix), they used data from census and land records, and Foursquare archives.
The research finds that Rome and Milan have completely different land use mixes, which leads to different outcomes. Milan is diverse. Rome is more homogeneous with districts that are only residential, commercial, or industrial. "Consequently, in Milan, vitality is experienced only in the mixed districts," the authors write.
The Italian cities meet Jacobs's criteria for short blocks that promote walking. The cities have "dense streets, which, in fact, slow down cars and make it easier for pedestrian to cross, creating what Jane Jacobs called the 'sidewalk ballet'," the paper says. "This ‘ballet’ goes beyond simple pedestrian activity. It is about informal contacts and public trust."
In an interview, De Nadai and Staiano say their method could be used to understand whether projects—say, building a new park or pedestrianizing a certain area—have had the desired effect. "Using this methodology it would be possible to quantify the effect of interventions. After ten years, you could say whether it was a good decision or a bad decision, not as a matter of interpretation, but because of the data," they say.
And which Italian cities best meet Jacobs's rubric for a vital city? They say Milan and Turin exemplify it best. Palermo the worst. But then all six Italian cities are likely more to Jacobs's idea of an ideal city than some car-centric, big-block, new-build American ones.