Tomenable, this is going to be an average of self-selected gedmatch users, thus, people who are interested in their genetics and are pretty sophisticated about it, so just on its face it's not going to be representative necessarily of the real dominant ancestry of each state, right?
Given that, there will be virtually no Blacks or Hispanics, and even the averaging of the "white" testees won't necessarily give an accurate picture. It won't be completely off for Americans from states like Utah and other western states, Nebraska, Wyoming, Maine, the southern states (other than that you won't see all the blacks), places like that, or, in other words, states that are still pretty homogeneous and mostly descended from the original "Colonials". Some heavily German and Scandinavian areas in the Upper Midwest would show that ancestry but of course the similarities are going to be changed because they are going to be averaged with French Canadian, Irish, Polish, Italian etc. gedmatch users from those areas if there are any.
It's going to be inaccurate for states like Massachusetts, New York, Rhode Island, Ohio, Pennsylvania, California, Texas etc. Trust me, the people in New Jersey are not mostly Friulan like.
What happens with the averaging is that Southern Italian gedmatch users mixed with Irish and English gedmatch users and a few Poles thrown in is going to give you a far northeastern Italian.
The largest population group in Texas, if not now, then soon, will be Hispanic, mostly Mexican. In Massachusetts, the Irish predominate, but there are English descent Yankees still there and a very large Italian-American community, as there is in Rhode Island and Connecticut. In New York, you have large populations of Blacks and Hispanics, especially in the Metro area, along with the Irish and Italians and Jews, but the rest of New York State is heavily English, German, and still Dutch from early settlement days, although even there you have large Italian communities in the Albany area and far in the west in Buffalo. Lots of Poles in Buffalo too. Pennsylvania is a mish-mash like that as well.
Someone mentioned Hawaii. Japanese people are the largest ethnic group, but there are also Chinese, as well as Polynesians, and people of English descent. Is the gedmatch group going to reflect that. If there are a few Japanese users and they're mixed with the usual English or German Americans, you might get Central Asians as the dominant group, right?
This analysis got some of the complexity, but even here it can be misleading: It doesn't show the Jews anywhere (most are where Italians are, generally), it doesn't show the Poles, it doesn't show all the English descendants in the "German" Midwest, or in the Hispanic areas such as in Texas or southern California, and it totally misses the complexity of places like Massachusetts, Pennsylvania, Illinois, and Ohio. Part of this "problem" with "English" ancestry, is that a lot of the descendants of "Colonial" Era Americans, just identify as "American" on census reports etc. There's also a lot of "mixed" people. Irish/Italian people should be their own category. Irish/German as well, especially in places like the Midwest and Pennsylvania, New York etc. People with more recent ancestry, like Germans, Irish, Italians, Jews, Poles, are more likely to identify that way than Colonial Era descendants identifying as English.
They do at least get the largest self identified population group by county, though.
Here's another view of it:
Just on Italians:
If you were to visit only the places where most Americans live, you might not see or appreciate some of this.