Half the world now lives in a city, for the first time in history — and the intellectuals are finally catching up with that fact. There’s New Yorker journalist David Owen, who points out that city living is environmentally friendly: the elevator is a far more efficient way to move people than the car. Ed Glaeser, a Harvard economist, uses a new book, The Triumph of the City, to argue that cities are the driving force of innovation and economic growth. And Black Swan author Nassim Taleb predicted recently that nation states would be supplanted by city states by 2036.The true radical of the field, however, is Paul Romer. Both a highly influential academic economist and a successful entrepreneur, he turned down the job of chief economist of the World Bank to champion his alternative approach to ending global poverty: so-called ‘charter cities’.