Most conspicuous, in my experience, is the way that retailers have responded. It’s not just CVS; coffee shops seem to have gotten more hostile and less welcoming. This is, I suspect, because they are dealing with people who steal, cause a ruckus, or shoot up in the bathroom—disorderly behaviors that they have to deter before they cost them customers.

I increasingly think this is a more general phenomenon. Disorder is not measured like crime—there is no system for aggregating measures of disorder across cities. But if you look for the signs, they are there. Retail theft, though hard to measure, has grown bad enough that major retailers now lock up their wares in many cities. The unsheltered homeless population has risen sharply. People seem to be controlling their dogs less. Road deaths have risen, even as vehicle miles driven declined, suggesting people are driving more irresponsibly. Public drug use in cities from San Francisco to Philadelphia has gotten bad enough to prompt crack-downs.

Cities’ comparative advantage is agglomeration and network effects: concentrating people in one place can create innovation that yields ore than linear returns. But that only is possible if people have shared public spaces in which to interact. Community life, of the sort that makes cities worth living in, is harder to live in the presence of disorder.

A large share of disorder is generated by a small number of people and places—one drunk or one vacant lot, one uncontrolled bar or one guy shouting on the street, can ruin the whole experience for everyone else. Identifying these problem places and people, and remediating them—not exclusively through the criminal justice system—can bring disorder under control.