Lumpy

From Why the Ideological Melting Pot Is Getting So Lumpy by Shankar Vedantam:

Americans like to live in diverse communities. At least, that's what they say.

About two in three Americans say they prefer to live around people belonging to different races, religions and income groups. In reality, however, survey research shows that people are increasingly clustering together among those who are just like themselves, especially on the one attribute that ties the others together -- political affiliation.

A consequence of such polarization is that large numbers of Americans no longer have much contact with people belonging to the other party. Many feel the views of their political opponents are not just wrong but incomprehensible.