More than just corresponding to population, it seems that the hot spots correspond to “semi-urban areas”. The densest pop areas seems to cool off a bit.

My theory -

1) The psychology motivating “hateful” tweets in inversely proportional to population. It is an anti-social behavior that is mitigated by exposure to other people, and is strongest in rural areas.

2) Number of tweets in general is proportional to population. More people equals more tweets because there’s more people to do it but also because urban area tend to lead in adoption of new tech. (And by tech I don’t mean just Twitter, but the diverse array of platforms used to access Twitter.)

3) Thus, the hottest areas are where these two inverse factors come together at a kind of midway point.