Ed Glaeser is a economist at Harvard, and the author of Triumph of the City, and as his business casual look he wears a bow-tie with ice-cream cones.

He is also one of the world’s experts on the nature of cities, and he was invited to set the stage for the TED2012 wish.

“At their heart,” he says, “cities are the absence of physical space between people.” And cities are powerhouses of the economy: The three largest metropolitan areas produce 80% of GDP but contain only 13% of population.

Glaeser talks about how, in the 19th century, Americans moved into the vast continent, and spread out. In the 21st century we’re moving closer together and taking advangtage of the benefits of being close to each other, and cities are growing tremendously. But if cities in the developed world are growing, that is nothing compared to the growth of cities in the devloping world.

More than half of humanity now lives in cities, and it’s been incredible successful. The countries with populations more than 50% urbanized have incomves 5 times higher and infant mortality three times lower than countries that haven’t passed that. Glaeser quotes Gandhi, The future of India in its villages not in its cities,” and adds, “With all great respect, the man was deeply wrong. The future of India is very much in its cities.”

In Glaeser’s youth in New York City in the 1970s, it really seemed like cities were dying, “it really seemed possible that all of America’s older cities would revert back to some planet of apes like wilderness” After a Boeing layoff in Seattle, two jokers put up a sign saying, “Will the last person to leave Seattle please turn out the lights.”

All of that decline was because it looked like cities had lost their economic reason for being: Transportation. In the early days of the United States, it cost as much to ship 30 miles over land as to ship across the Atlantic. So cities emerged as nodes on a transportation system. As transportation became cheap, industry fled. Looked like cities were doomed.

The other real problem, was urban sprawl. “Each new highway that cut into an urban core reduced the city’s population by about 18% relative to the rest of the area.” Federal government pursued a strategy that ignored the real heart of a city: the people. Infrastructure isn’t what’s needed. The variable that explains which cities came back is human capital: The schools and average education level.

And cities are a wonderful place to take advantage of being close to other humans. New technologies and globalization have increased the returns from being smart, and we get smart by being around each other. “We have marvelous cues for communicating that are lost when you are not in the room. Harvard grads want to go to Silicon Valley, because you can’t learn to be a software engineer by reading Wikipedia.”

The most entrepreneurial place Glaeser has seen is the Dharavi slum in Mumbai. He saw people doing all kinds of creative things, and he marvels at the energy, but he also marveled at the public failures. There are downsides to cities, and cities have been battling them for centuries. Some of these problems need more than just an engineering solution. If you build cars, people will drive. You can’t engineer out of that, you need to do like Singapore, which charges people for congestion.

When cities can deal with those problems, they can be incredible and wonderful places to live. Density can cover fixed costs of museums and theaters.

“The world should embrace its cities.”

Photo: James Duncan Davidson