Vertically inclined cities could make a lot of money allowing private developers to build high-rise apartments or business spaces above libraries, city halls and schools.

Public works projects often come at heavy expense. Whether it’s building new schools, municipal halls or other facilities, such projects produce not only upfront costs, but depending on their magnitude, long-term debts. There is, however, a way to mitigate costs, or even make a project more profitable: Sell off the air rights.

This is an idea that, while holding vast economic potential, is used sparingly in America. Nowadays whenever cities build a central library, to name one example, they usually construct a single-use facility that is only a few stories tall, if that. But what if, before such libraries were built, the air rights — the undeveloped space above the roofline — were deregulated and sold off? In expensive and vertically inclined U.S. cities, private developers would pay governments enormous sums for the right to build a high-rise apartment complex or business space above public projects. This would lead to the broad maximization of public land values, and thus to enormous cash windfalls for local governments.