If we consider flybe/Stobart Air know what Northern Europe is, then we may be talking about a very few airports: airports in Denmark (EBJ and AAL are the only with no flights to STN), airports on the south west coast of Norway (SVG and BGO) and one airport on the west coast of Sweden (GOT). All these airports mentioned are less than 600 nautical miles from SEN, which I think a maximum leg length should be for the ATR.
Compass point divisions of Europe are a movable feast. For half a century it was an alleged "east-west" (iron curtain) communist/non-communist divide, and much of central Europe was described as "east" Europe.
Now it's a "north-south" divide, linked to the eurozone problems with the "south" in trouble and the "north" (mostly) outside the eurozone.
The whole thing is subjective and movable and a matter of attitude and perception. Let's not get to hung up about it.