The people who design and build cities have a saying, or they used to: The mistakes of the planners are inherited by the health department. When basic city functions fail, people get sick.

So it makes sense, in a syllogistic sort of way, that the converse might also seem true: If people get sick in a city, the planners must somehow be at fault. When 193,000 people test positive for Covid-19 and nearly 16,000 die in New York City, the densest major urban concentration in the United States, maybe the closely woven fabric of the city itself is to blame. Both Governor Andrew Cuomo and Mayor Bill De Blasio said it straight-out: New York’s density makes it especially vulnerable to a respiratory disease pandemic—all those people crowding into subways, skyscrapers, studio apartments, Brooklyn coffee shops, and presumably Greenwich Village hep-cat jazz boîtes, asymptomatically exhaling the virus on each other and causing a catastrophe that could play out again in city after city without some posthaste suburbanization. “There are mechanistic reasons we would expect there to be more transmission in places where the population density was higher,” says Linsey Marr, a Virginia Tech researcher who studies airborne virus transmission. “I think there are more opportunities for transmission.”