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No, it’s not the cronut or the Old Bay Doughnut Chicken Sandwich. It’s more of a double doughnut. And it’s a lot less caloric, but arguably more important, than its trendy relatives.

Twenty-five years ago, the doughnut theory of urban studies went like this: Cities were poor (the doughnut hole) and suburbs were rich (the doughnut). But the model has shifted over the past quarter century, to the point where wealthy cities are now surrounded by poorer inner suburbs (populated by people who can no longer afford the city), which in turn are surrounded by wealthier outer suburbs.

A new study from the University of Virginia quantifies this concept by plotting various demographic characteristics against the distance from the center of a city. In D.C.’s case, as in many cities around the country, the results are striking.

See the chart above. In 1990 (the orange line), the wealthiest area of the D.C. region was about 12 miles outside the center of the city (defined in this study as a spot in the middle of the National Mall)—-say, around Vienna or McLean or Potomac. In 2012 (the brown line), the wealthiest spot is the city center area itself. In fact, everywhere in the region has gotten wealthier except that ring about 12 miles from the center. Then there’s a second, smaller peak about 17 miles from the center, around Burke or Fairfax or Bowie.

There are similar trends for other demographic measures. Here’s educational attainment …

… and young adults’ share of the population:

Population density has risen nearly everywhere, but particularly near the city center, while it’s remained flat about three to five miles from the city center in outlying D.C. neighborhoods like Tenleytown and Michigan Park and Benning:

Meanwhile, there’s been a racial shift, with areas near the city center whiter than before (and, in fact, majority white) and most other areas blacker than in 1990:

Incomes and education levels have risen within five miles of the city center—-but they’ve actually declined in the inner suburbs surrounding D.C.:

The doughnut, however, is a bit lopsided. As Luke Juday, the author of the study, noted in a report last year, the demographic numbers change considerably depending on whether you move east or west from the White House. Income and education levels are highest at the city center, but the dropoff is gradual as you head west. Moving eastward, on the other hand, brings a sharp decline in these numbers:

If you got a doughnut this misshapen at the store, you’d send it back. If you get it in urban studies, it’s just another example of the messiness of demographics. But the trend is still overwhelmingly clear, even if it hasn’t played out the same way everywhere.

Images courtesy of the Demographics Research Group at UVA