This map looks more like the result of a highschool project, not Harvard published data. I wish they would have linked the specific sources and labeled more on the map.
Without looking at their data, I can vouch that this sort of data may be prohibitive to access. The players involved don’t see data as something to be given out freely IME. It’s probably provided in a technically difficult to parse way-just to add insult to injury. Enough so that the simplicity of the presentation is remarkable.