What cities have precincts that meet this criteria?
As stated elsewhere, the first place I noticed this was of all places Des Moines, Iowa. St. Paul has a large cluster of precincts that meet the criteria, making up almost a 1/3 of the city's population together. Other places I'd expect to have such precincts include San Francisco and maybe some other Bay Area city, Los Angeles, NYC and maybe Honolulu if it has any areas of concentrated black population. What places can be confirmed?
10% is really too low of a threshold.
There are 11 in Travis, and 8 in Denton. Too many to count in Harris.
Precinct 620 in west Houston: 34% Anglo, 22% Hispanic, 22% Black, 21% Asian.
Sum of Squares: 0.251
