The expansion of digital record keeping by police departments across the U.S. in the 1990s ushered in the era of data-driven policing. Huge metropolises like New York City crunched reams of crime and arrest data to find and target “hot spots” for extra policing. Researchers at the time found that this reduced crime without necessarily displacing it to other parts of the city—although some of the tactics used, such as stop-and-frisk, were ultimately criticized by a federal judge, among others, as civil rights abuses. The next development in data-informed policing was ripped from the pages of science fiction: software that...