In 1539, when the Carta Marina was published, a short key to the map was printed to accompany it. The key was printed in an Italian edition with the title Opera breve and in German as Ain kurze Auslegung und Verklerung der neuuen Mappen. Both of these short pamphlets are reproduced in facsimile in the book by Herman Richter, Olaus Magnus Carta Marina 1539 (Richter, 1967). These are the first keys to the map, published with the map. They have brief explanations of features on the map.

The map was soon very rare; more copies of the two keys were available than copies of the map itself. Before long these keys were the only record of the existence and content of the great wall map.