EDWARD GLAESER: "What these new forces have done is they've increased the returns to new ideas, to being smart, because now if you got a new idea, you can manufacture it on the other side of the planet, you can take advantage of some new market opportunity in India, or Indonesia or Sub-Saharan Africa. These trends have also made cities more important because cities are at their heart today, engines of innovations, forgers of human capital."

Edward Glaeser has written a new book called "Triumph of the City." He takes readers on a world tour of what he considers urban success stories, from Boston, London and Tokyo to Bangalore and Kinshasa.

Mr. Glaeser is a professor at Harvard University. He himself lives outside the city of Boston.

Big cities can seem impersonal. They can be crowded, dirty and dangerous, but also places of pleasure and production. Mr. Glaeser says restaurants, supermarkets, theaters and museums all play a part in creating jobs.

EDWARD GLAESER: "If you look across the world, the countries where more than half of the people live in urban areas are more than four times richer on average than the countries where less than half of the people live in urban areas."

Mr. Glaeser says areas of poverty in cities are really a sign of the power of cities.

EDWARD GLAESER: "Cities don't make people poor, they attract poor people. And they attract poor people by delivering a path out of poverty and to prosperity, a chance to partner with people who have different skills, access to world markets, access to capital that enables poor people, some of them -- not all of them -- to actually find a way forward."