When world leaders, economists, and pundits talk about global economic power, they usually talk about nation-states. That’s how we typically tally up economic power, rating and ranking nations on their gross domestic product. Today, economists and business analysts talk about when China will overtake the United States as world’s largest economy (based on at least one measure of purchasing power parity it already has).

But this obsession with nation-states does not fit the reality of today’s highly-clustered knowledge economy, centered in and around global cities. And, it’s not just individual cities and metropolitan areas that power the world economy. Increasingly, the real driving force is larger combinations of cities and metro areas called mega-regions.

Back in 1961, the economic geographer Jean Gottmann coined the term “megalopolis” to describe the emerging economic hub that stretched from Boston to Washington, D.C. The term came to be applied to a number of regions in the world, including the vast Midwestern megalopolis that extends from Chicago, through Detroit and Cleveland, and south to Pittsburgh, which Gottmann dubbed “Chi-Pitts.”