Extending far beyond a single core city and its surrounding suburbs, a mega-region is an area that hosts business and economic activity on a massive scale, generating a large share of the world's economic activity and an even larger share of its scientific discoveries and technological innovations.

While there are 191 nations in the world, just 40 significant mega-regions power the global economy. Home to more than one-fifth of the world's population, these 40 megas account for two-thirds of global economic output and more than 85% of all global innovation.

The world's largest mega is Greater Tokyo, with 55 million people and $2.5 trillion in economic activity. Next is the 500-mile Boston-Washington corridor, with some 54 million people and $2.2 trillion in output. Also in the top 10 are mega-regions that run from Chicago to Pittsburgh, Atlanta to Charlotte, Miami to Tampa, and L.A. to San Diego. Outside of the U.S., you can find megas around Amsterdam, London, Osaka and Nagoya, Milan, Rome and Turin, and Frankfurt and Stuttgart.

Mega-regions are the true force driving the rise of emerging economies. Some 40% of Brazil's total economy is made up of a corridor stretching from Rio to São Paolo. Russia is propelled by the Moscow mega. India's economy is shaped by the mega-regions of Bangalore and Mumbai.

However, there are some problems for the mega regions. Much of public policy not only ignores the rise of the mega-regions, it actually works against them. If we want to bolster economic competitiveness and ensure long-run prosperity, we must pursue policies that take mega-regions into account. First of all, that means remaining committed on global trade. Second, it's time to stop transferring wealth from the most productive mega-regions to lagging places. Also, public policy must work toward, not against, density.