What can you learn from looking closely at a city? Get down to street level, and you can see how people conduct business, how they raise their children, how they fall on hard times and what helps pull them out. When Robert Sampson was an urban sociologist at the University of Chicago, he spent 12 years learning about the city’s residents and institutions—analyzing the work of its police officers, politicians, religious leaders, real estate agents, and school principals, and writing papers that helped make sense of city problems from violent crime to teen pregnancy.