There were questions about the actual content of the map. Witten had pointed out that it bore strong resemblances to a map made in the 1430s by Italian mariner Andrea Bianco, but others found some of the similarities and differences very strange—the map cuts off Africa where Bianco's map has a page fold, but distorts shapes, and includes major revisions in the far east and west. The most surprising revision is that, unlike, for example, the famous Cantino World Map, the Vinland Map depicts Greenland as an island, remarkably close to the correct shape and orientation (while Norway, of which Greenland was just a colony, is wildly inaccurate) although contemporary Scandinavian accounts—including the work of Claudius Clavus in the 1420s—depict Greenland as a peninsula joined to northern Russia. For practical purposes, Arctic sea ice may have made this description true, and Greenland is not known to have been successfully circumnavigated until the 20th century. Skelton wondered also whether the revisions in the far east were meant to represent Japan—they seem to show not only Honshu, but also Hokkaido and Sakhalin, omitted even from Oriental maps in the 15th century.