Mason Dixon Line
The boundary between Maryland and Pennsylvania. A symbolic dividing line between the North and the South before the Civil War. The two surveyors who mapped the line, Charles Mason and Jeremiah Dixon, are the namesake for the imaginary border.
Example:
Once you've crossed the Mason Dixon line headed North, you're not likley to find a Waffle House.
Once you've crossed the Mason Dixon line headed North, you're not likley to find a Waffle House.