Marry merry Mary?

Here are some beautiful maps showing the way pronunciation and usage vary across America.

For me, the oddest result was the map showing that I live in a small area of the country that pronounce Mary, marry, and merry differently.  Can that be right?  Of course they’re all pronounced differently!  On the other hand, I can’t hear any difference between Don and dawn, which I read somewhere are obviously different.

I was also baffled by a couple of regionalisms that they omitted.  There’s a map showing regional variations in the word used for soda, but they don’t include tonic for New England.  I suppose that usage is dying out.  But the word rotary for roundabout or traffic circle isn’t dying out.  Why don’t we get credit for that? Look, we even put the name on signs:

A rotary in Lowell, Massachusetts.

(There is an absurdly long Wikipedia article about roundabouts.  Someone must really care about them.)