In a lot of cities especially, COIs will mirror sharp political divides. NYC is a prime example of this.
As is often the case, New York City is a poor example because it is unlike other American cities. Most American cities do not have Republican areas: there is not a single Republican precinct with more than ten votes in Boston or St. Louis or Minneapolis or Seattle. In the whole city of Los Angeles in 2020 there were exactly two.
Fair, but in cities like MSP and Seattle, you can see a really stark dropoff in D% between the precincts at the edge of the city and precincts outside the city, even if overall everything is safe D.
NYC is prolly just the clearest example.
