Ex, I googled the same damn thing yesterday. Can't remember why . . . but I did.
First off, I have to define "diverse". In the way we're talking about it, it's much more than an academic definition. For what we mean, it signifies many different cultures coming together, living amongst each other, learning from each other, having relationships, etc. For me, it means that the sum is greater than just adding all the individual parts together.
I thought that this map was WAY off, though. Why? Well, look at what they say about a country like Uganda. "They are diverse because they have over 100 different tribes." OK, but that doesn't make them "diverse". It makes them "divided". Do those tribes intermingle, intermarry, and live amongst each other? If not, then they aren't really diverse - in the meaning that we are talking about it. It's just coincidence that someone drew a line around a lot of tiny, isolated villages. Or, if they do intermingle, intermarry, etc., then they still aren't diverse, because they are all 1 race - African American. From Africa. Living in Uganda.
For further explanation, look at that comparison the CIA made for German and USA that Fstar posted. German? Italian? Polish? They're all f**k WHITE! Uganda had all those other tribal names, when it should have said "99.999999% African (with 3 white dudes who got lost on vacation)".
But, let's look at "American" for a sec. If we applied the Ugandan structure, then we'd be 2.6% New Yorkian, 1.1% Los Angelian, 0.9% Chicagan, 0.8% Houstonian, etc. And, that's just stupid.
Lastly, I don't think America is the "most diverse". But, I think we're up there. Canada surely might have us beat, though I'd find it hard to believe that there are as many "other-than-white" in Canada as in America. But, I've never lived there, only visited. Sure looked pretty white to me, though. Mexico? Perhaps, but they all speak Spanish, eat similar foods, are probably Catholic, etc. regardless of their country of origin.
I guess my main takeaway from all this is that . . . whatever criteria is used, I'm going to have a problem with it. In order to do this kind of exercise, you have to draw lines. But, where? At what point is someone black or white? How can you be both Latino and black (I know how - but statistically, it screws up the system). What if my mother was black but from England, my father Asian from Indonesia, both had immigrated to South America, and I was born in India? Can I just color the whole sheet in?