File talk:Most common ancestry in the United States by county.png

What is this map based on? It looks like this map except merging "English" and "American": https://upload.wikimedia.org/wikipedia/commons/thumb/a/a7/Census-2000-Data-Top-US-Ancestries-by-County.svg/2000px-Census-2000-Data-Top-US-Ancestries-by-County.svg.png