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If Buildings Were Molecules, Then New York Would Be a Crystal and Boston an Amorphous Liquid

An engineer at MIT may have cracked one long-standing question: How do you describe a city’s structure?

ByTim De ChantNOVA NextNOVA Next
Boston's organic development through the years gives it a structure similar to an amorphous liquid.
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Cities, for all their complexities and idiosyncrasies, have long defied scientific description. But Franz-Josef Ulm, an engineer at MIT, may have cracked one long-standing question: How do you describe a city’s structure?

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The answer came to Ulm when he was idling studying an aerial photo of a city during a coffee break. The pattern, he realized, looked a lot like the molecular structures he studies in his research on the small-scale mechanics of materials like concrete, rocks, and bones.

Inspired, he began to map out different cities’ buildings, noting how they were clumped, where they were most dense, the overall pattern they created, and more. From that, he could classify each city like he would a material. Boston, with its long history and organic, disordered development, resembles an amorphous liquid, he says. New York, with its high density and regular street grid, has a crystalline structure.

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Ruth Graham, reporting for the Boston Globe, dives into the details behind Ulm’s work:

In physics, an “order parameter” is a number between 0 and 1 that describes how atoms are arranged in relationship to other atoms nearby; Ulm applies this idea to city layouts. Boston, he says, has an “order parameter” of .52, equivalent to that of a liquid like water. This means its structure is notably disordered, which may have something to do with how it developed. “Boston has grown organically,” he said. “The city, in the way its buildings are organized today, carries that information from its historical evolution.”

Much of that historical information is lost when you distill a city down to a number, but Ulm and his colleagues are hopeful that their approach can provide a starting point for scientists to build up to more complex rules that describe how cities function.

Some planners are skeptical that such a simplification will be useful, but as Graham points out , Ulm isn’t alone in attempting to determine the mathematical relationships of urban areas; the movement appears to be gaining momentum. Someday, we may finally be able to decipher the city, one of the greatest feats of human ingenuity.

Photo credit: USGS