RAP MAP.(The Talk of the Town)

From water pipes to porn shops, cartographers have charted almost every aspect of local urban life, giving rise to a sort of cottage industry: the New York City specialty map. The latest--and one you are not likely to see unless you run in criminal-justice circles--is a rendering of the city that breaks down, block by block, the home addresses of all New Yorkers incarcerated in a given year. This map won't get you from Century 21 to the Met. But it does reveal that more prison-bound Bronx residents lived in walkups than in any other type of building, that Staten Island is the most law-abiding borough, and that Brooklyn--nicknamed "the borough of churches"--ran up the state's highest bill in prison costs.

Eric Cadora and Charles Swartz, co-founders of the Brooklyn-based Justice Mapping Center, collaborated on the project with an architect named Laura Kurgan, at Columbia's Spatial Information Design Lab. "What started out as a scholarly inquiry has turned into a national initiative," said Cadora, whose team has mapped twelve cities so far. Their New York is a digital crazy quilt of "bright-against-black": the areas least touched by incarceration in 2003, the year they chose to study (Riverdale, Bay Ridge, the West Village), appear black and gray; those more so (Coney Island, Bedford-Stuyvesant, Hell's Kitchen) neon orange.

Recently, the mapmakers gathered at Columbia, and Cadora, a substantially built man with a fondness for Camel Lights, turned the face of his laptop to reveal the map. "Zero-value areas"--places where no one went to prison--were shaded black. "You see them crop up all across the city, but they never make up an entire neighborhood," he said, invoking what might otherwise be a bragging point among New Yorkers: "There is always something going on somewhere." The exceptions? "What I jokingly call 'the Mafia neighborhoods' of South Brooklyn," he said, "where you've got one or two guys going away from an entire neighborhood. Also, this." He pointed to a dark strip of the Upper East Side--the blocks in the Seventies and Eighties that border Central Park.

Just above was Harlem, the area with the highest rate of incarceration in the city: forty-four ...