If the islands on the western edge of the 1424 Nautical Chart are thought to be real, what lands do they represent? After all, the chart dates from 1424, many decades before 1492 and Columbus. Does the 1424 Nautical Chart document European knowledge of America prior to Columbus?

The Canepa, Roselli, and Pizzigano portolan charts in the James Ford Bell Library all have islands in the west. These chart makers were from different places (Genoa, Majorca, and Venice) and made their charts at different times, 1489, 1466, and 1424.

The appearance of islands on all of the charts indicates continuity at the very least. Why should these islands stay on charts for such a long time if there was no substance to them? Perhaps the later charts were modeled after the 1424 chart, or a chart made even earlier that has not survived. Do these islands represent myth and legend? Who has tried to answer these questions, and how?