What he pointed to was an interactive map that displayed ethnically color-coded dots for each household based on 2010 census data. Many urban centers of population are diverse as a whole, but within the cities are distinguishable communities grouped by ethnicity.
Some may be startled by the fact that communities within these cities almost draw metaphorical borders on ethnicity, but some may take it as nothing special. What are the circumstances for this phenomenon?
Are economic circumstances driving certain ethnic groups toward certain areas of a city? Recent data shows that Latinos and African-Americans are generally on the lower end of the income bracket as a whole, which may drive them toward higher-density urban housing. But again, within urban areas are distinct communities between ethnicities.
Do people just want to simply be part of their own culture? Maybe, but do they make that decision consciously when choosing where to live?
The entire interactive map can be used here.
Here are three examples; Los Angeles, San Diego, and New York City: