In highly skilled societies, bigger cities are associated with higher levels of productivity and income, the column explains. This seems to be due to the ways in which cities facilitate innovation in an age of rapidly increasing economic and technological complexity. Prosperity now requires lots of skilled individuals in reasonably close proximity to each other, to learn from and occasionally partner with as part of the process of coming up with and spreading new ideas. America appears to be better able than Europe to accomplish this across a wide range of places.
Read more here.
Also check out Ed Glasser's Triumph of the City: How Our Greatest Invention Makes Us Richer, Smarter, Greener, Healthier, and Happier. Highly recommended!