“It’s a megalopolis of eggheads,” said William H. Frey, a demographer with the Brookings Institution. Frey said Washington is an example of how the country is compartmentalizing itself into clusters of people with different backgrounds and world views.

“It’s a magnet for people who grew up elsewhere and came here because they want to be in a place that has an atmosphere of intellectual curiosity. But it means we’re somewhat isolated. A lot of people here may study and advocate for what’s going on in the rest of the country, but they can’t feel what’s going on if it doesn’t touch them.”…

Although the wealthiest Americans have always lived in their own islands of privilege, sociologists and demographers say the degree to which today’s professional class resides in a world apart is a departure from earlier generations. People of widely different incomes and professions commonly lived close enough that they mingled at stores, sports arenas and school. In an era in which women had fewer educational and professional opportunities, lawyers married secretaries and doctors married nurses. Now, lawyers and doctors marry each other.

A recent analysis of census data by sociologists Sean Reardon of Stanford and Kendra Bischoff of Cornell highlighted how middle-income neighborhoods have been fading away as more people live in areas that are either poor or affluent.

In 1970, 65 percent of families lived in middle-income neighborhoods; four decades later, 42 percent did.