By Alice Goffman, from On the Run: Fugitive Life in an American City, to be published next month by University of Chicago Press. Goffman, a sociologist at the University of Wisconsin–Madison, spent six years living in Philadelphia’s Sixth Street neighborhood, studying the effects of drug policing and the techniques residents use to avoid arrest.

Rakim, a rotund man in his forties, ran a photo stand in downtown Philadelphia, near the customs office. A large sign reading passport pictures, cheapest in the city welcomed patrons inside. On the first afternoon I went to see him, a…