Passage: The few expeditions to penetrate much beyond the Arctic Circle in this era added only small islands, such as Novaya Zemlya (11th century) and Spitzbergen (1596), though since these were often surrounded by pack-ice, their northern limits were not so clear. The makers of navigational charts, more conservative than some of the more fanciful cartographers, tended to leave the region blank, with only fragments of known coastline sketched in.

Question: What did cartographers tend to do?
leave the region blank