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.”

But mega-regions are hard to identify using traditional data sources. About a decade and a half ago it dawned on me that you can actually see mega-regions like the Boston-New York-Washington corridor when you pass over them in a plane at night. So my colleagues and I undertook a project to identify the world’s mega-regions from these satellite images of the world at night.

Using this new and improved satellite data from 2015, we define mega-regions as areas of continuous light that contain at least two existing metro areas, have populations of five million or more, and generate economic output of more than $300 billion. (We add up population and economic output data on a purchasing power parity basis for mega-regions using base data from Oxford Economics via Brookings’ Global Metro Monitor). In two well-known U.S. cases, we form mega-regions out of two relatively distinct satellite footprints: Chi-Pitts, as well as the Texas Triangle of Houston, Dallas, and Austin.

We ultimately identify 29 mega-regions as the real regional powerhouses of the global economy. Eleven are in Asia, 10 are in North America, six are in Europe, one is in Latin America, one is in Africa, and one more straddles Asia and Africa. My CityLab colleague David Montgomery made the maps of these mega-regions.

• Bos-Wash, which extends from Boston through New York and Philadelphia down to Washington, D.C., is the world’s largest mega-region of nearly 50 million people, generating almost $4 trillion in economic output.  If this mega-region were its own country, the economy would be equivalent to the world’s seventh largest, bigger than the United Kingdom’s or Brazil’s.
• Par-Am-Mun: Coming in second, this European mega-region spans Paris, Amsterdam, Brussels, and Munich. Home to 44 million people, it generates $2.5 trillion in economic output, about as much as Mexico does and more than Italy, equivalent to the world’s sixth largest economy.
• Chi-Pitts: In third place is this great heartland mega-region which runs through Minneapolis, Chicago, Indianapolis, Detroit, Cleveland, and Pittsburgh, encompassing 50 metros large and small, in total. With a population of more than 30 million people, this mega-region produces more than $2 trillion in economic output, comparable to South Korea’s, making it roughly the 14th largest economy in the world.
• Greater Tokyo is Asia’s largest mega-region, generating just under $2 trillion in economic output and home to almost 40 million people. Its economy is comparable to Spain’s and larger than Canada’s. It would rank as the world’s 11th largest economy if it was a country of its own.
• SoCal, running from Los Angeles to San Diego, is home to more than 20 million people and produces nearly $1.5 trillion in economic output, comparable to the economic output of Australia, and among the world’s 20 leading economies.
• Seoul-San is the world’s 19th largest mega-region. Running from Seoul to Busan, it is home to the 36th largest economy in the world.
• The Texas Triangle spans Dallas, Houston, and San Antonio as well as Austin. It generates $1.2 trillion in economic output while housing just under 20 million people. It would rank as one of the world’s top 25 economies.
• Beijing-Tianjin is China’s largest mega-region. With nearly 40 million residents, it also produces $1.2 trillion in economic output, putting it, too, among the list of the 25 largest economies in the world.
• Lon-Leed-Chester: This mega-region which runs from London through Leeds, and Manchester also generates $1.2 trillion in economic output while housing more than 20 million people. It too makes the list of the world’s top 25 economies.
• Hong-Shen combines Hong Kong and Shenzhen, home to 20 million people. The region creates slightly over $1 trillion in economic output, equivalent to the 26th largest economy in the world.
• NorCal consists of San Francisco, San Jose, and other Bay Area cities. With more than 10 million residents, it generates almost $1 trillion in economic output, making it the world’s 27th largest economy.
• Shang-zou: Spanning Shanghai and Hangzhou, this mega-region is home to nearly 25 million people and produces nearly $900 billion in economic output, placing it among the top 30 economies in the world.