What is "semslinie"

The Semslinie is a part of the border between the Dutch provinces of Groningen and Drenthe that runs right through the former Bourtanger Moor. The almost straight line runs from Wolfsbarge to the Huis ter Haar at Musselkanaal. The border is slightly bent at Stadskanaal. The slightly bent line between Musselkanaal and Stadskanaal is sometimes called Koningsraai. The Semslinie is named after Johan Sems.