We are a city of 8 million people, give or take a few hundred thousand. But we are building a city for 9 million. Literally. Right now. That will be New York City’s total population just a couple of decades hence, and politicians, bureaucrats, developers, architects, and engineers are, as you read these words, figuring out how to fit another million people onto the collection of islands and peninsulas we call home. We can’t just bulldoze and slap up some towers—we’ve learned some lessons from the sixties—and it isn’t just half a million new homes that we need. Those million need offices, factories, labs to work in. They need subways, buses (and ferries and trams) to commute in. They need places to park and places to play, plus the power to light their homes. All in a city that can’t sprawl.