The two gravest challenges facing America today, economic inequality and geographic divides, are increasingly intertwined. Economic inequality has surged with nearly all the growth being captured by the 1 percent, and the economic fortunes of coastal superstar cities and the rest of the nation have dramatically diverged.

These two trends are fundamental to a new study by Robert Manduca, a PhD candidate in Sociology and Social Policy at Harvard University. The study uses census microdata culled from 1980 to 2013, and finds that America’s growing regional divide is largely a product of national economic inequality, in particular the outsized economic gains that have been captured by the 1 percent.

Up until now, most researchers have believed America’s rising geographic divides to be a consequence of the way people sort themselves by education, occupation, and income. In Bill Bishop’s influential book, The Big Sort, the basic idea is that more skilled, affluent, and educated Americans move to the booming parts of the country—superstar cities like New York and Los Angeles and tech hubs like San Francisco, Seattle, and Boston—leaving the rest stuck in less-advantaged parts of the country.

To some, this is simply the effect of the clustering of talent and skill. For others, it is the result of the preferences of advantaged groups for amenities and other lifestyle factors. Some also say it is the consequence of land-use restrictions, which limit the development of economically successful places, or other barriers to growth.

Manduca does not deny that these kinds of geographic sorting forces are in play. Instead, he finds that the staggering growth in the economic divide helps to magnify such spatial division. The rich and the poor occupy different places to begin with, so as income inequality rises, the geographic discrepancies also rise as a consequence, with rich places getting richer and poor places falling further behind. Or as he puts it: national inequality acts like a powerful wave that “washes over an uneven landscape, leaving behind deep pools in some areas and shallow puddles in others.” The rise in economic inequality, even though not inherently spatial, does in fact have spatial consequences.

This growing pattern of spatial inequality can be clearly seen in the maps below. In 1980, there were only two U.S. city-regions, Washington, D.C., and the New Jersey suburbs of New York City (in dark blue on the map), where mean family income was more than 20 percent higher than the national average. Most of the rest of the map is shaded in gray (indicating mean family income ranges between 10 percent higher or lower than the national average) or light red, with some pockets of dark red.

Read the rest of the Richard Florida’s article at CityLab