A huge map of American English Dialects

[Spider Jerusalem]

5. Interesting but incomplete

it doesn't make note of the three-way distinction between Mary/marry/merry that exists for some speakers (mostly mid-Atlantic), nor of the preservation of minimal pairs in which/witch and whine/wine that also exists for some speakers (mostly Southern). Nor does it note the use of intrusive R in some dialects that are otherwise rhotic (Inland South/lower Midwest, and probably mostly among older speakers); my great-grandmother, who was from Louisville, Kentucky, pronounced "Washington" "Warshington", for instance. There's also no mention of yod-dropping (where "news" is pronounced "nooz", "loot" and "lute" are homophones, etc), which is not found in all North American English dialects (with Southerners again most likely to maintain the distinction). And the Canadian border doesn't actually represent a distinct isogloss for Canadian raising; elements of "Canadian raising" are found in Minnesota/North Dakota/Great Lakes areas (although it's not consistent).