It’s pretty flat. I actually spent a night in Flatonia about 30 years ago, when I was driving a U-Haul from Tucson to Gainesville, FL for my sister. We stayed at Grumpy’s (chose it because my nephew was getting cranky after a long day on the road).
I was in Pontiac Illinois (not Michigan) once and I swear it was about as flat as calm seas. It seemed you could actually see the next five miles of road