I found this map online via this page, and though the map seems fairly self-explanatory, I did not locate a page that elaborated on the map and the interpretation thereof.
What with all the discussion lately of 'Yankee culture' and its prevalence (or absence) outside New England, I thought this might be relevant. It looks to me as though 'Yankee culture' is confined to a couple of rather narrow geographical areas. I would even question the placing of the New England states, all of New York state, and parts of some adjoining states into that grouping. New England is not exactly home of Anglo-Saxon Puritan descendants now, as much as the descendants of 19th and 20th century ethnic immigrants (Italian, Portuguese, Jewish, French-Canadian) and recent immigrants from the four corners of the earth.