This paper deals with the onomastic representation of the Northern Ocean (encompassing the North Sea as well as the Baltic Sea) and its development during Antiquity and the Middle Ages. In the present account, Pytheas and Adam of Bremen will serve as beginning and end points, respectively. It will be demonstrated that names and their dynamics play a central role in the shaping of the mental landscape. The article focuses on the early island names Thule, Scandiae and Scadinavia, whose metamorphosis clearly coincides with a change of cartographic perception. This raises the question of a causal connection. In particular, the history of the island name Scandia appears in a new light against the background of Ptolemy’s cartography of Britain.