Commutes of two to three hours are common. Kidnapping is a booming business, and security is weak. But you decide it's worth it, because Mexico State is close to Mexico City. And Mexico City is the country's economic and cultural beating heart.

People in Westchester county feel the same way about New York City. That's where their jobs are. That's where they go out. Westchester is expensive, sure, but it's worth it to have access to New York without, you know, actually having to live in New York. And have you checked out those public schools lately?

Sure, the mansions and parks and well-maintained roads of Westchester are a far cry from the self-built houses and flooded sewers of Mexico State. But they are two sides of the same 21st-century coin: the megacity. New research suggests that only one of them is an environmental disaster—and it's not the one you think.