To be honest, first I looked at the headline on BB, and I thought “well, duh”. Then I looked at the map in the BB post, and I thought, “wait a moment, that map doesn’t really show anything beyond the fact that some areas of the US are more diverse than others”. Then I looked at the linked post.
There is also problem (3), which is that the US seems to be mostly made up of rich majority-white districts and poor majority-nonwhite districts. Problem (1) does not need any maps to show. Problem (3) alone is big enough.
How big is Problem (2) on top of Problems (1) and (3)? We need to look at individual counties to see that. And we need to compare the percentage of white students in majority-white schools in a county with the overall percentage of white public-school students in that county.
Now I have no idea whether the percentages shown in the mouseover on those maps refer to all students or to all public-school students. If they refer to all students, we will only ever see problems (1) and (3) in the map and we have no chance at reliably seeing problem (2). It’s covered up by the other two.
If they do refer to public-school students, then we really need to look at details. Why are there 100% white students in white schools in a district with 72% white students, and still 32% in a neighboring district with just 14% white students? Is that just a fluke or is it significant? A few districts over there are 31% white students, but 0% of them are in “white” schools.
Conclusion: The problem that the headline talks about cannot actually be seen from the maps without more statistical analysis. That’s why I was asking for different maps.