These dialect survey maps are interesting. Indiana is often split between a northern dialect and a southern one.
I grew up in northern Indiana and I often noticed differences in dialect there. My cousins lived in Plymouth, and I thought they had more of a northern accent than we did. Then when I went to college in Franklin, the locals there had much more of a southern accent than I did. After living in Franklin several years I guess I picked up that southern accent. One time when I went back to Rochester and was talking with someone I hadn't seen for several years, they asked me if I lived in Kentucky. I didn't think I had that much of a southern drawl!
In regards to this particular map, I say "may-uh-naze", but I remember Gram Booker, from northern Indiana, called it "man-aze".