As in environmentally friendly, to be sure. Not only are residents of dense cities far less likely to drive (and far more likely to walk), they take up less space and fewer resources (since infrastructure is easier to share in a dense environment).

But cities that are able to handle density are also quite green in a money-making, cash ka-ching sense. As concentrations of human capital, they facilitate most of the economic activity that makes the country go. Well planned density increases the city’s capacity and production potential. It can also reduce housing and transport costs, making individual workers more productive.

Sadly, cities are classic public goods, which means that while they’re wonderful for society, they’re underprovided by the market. To achieve optimal urbanization, government ought to subsidize density. It’s not a particularly popular idea, but it may come to be more accepted as resource pressure and suburban congestion become increasingly burdensome. And as New York continues to make itself an example of the value of urban life.