Changing World Views
Maps called "portolan charts" which feature coastlines, harbors, reefs and shoals were important for mariners.
As Waldseemüller wrote: "All that has been said by way of introduction to the Cosmography will be sufficient, if we merely advise you that in designing the sheets of our world-map we have not followed Ptolemy in every respect, particularly as regards the new lands, where on the marine charts we observe that the equator is placed otherwise than Ptolemy represented it" (Waldseemüller 1907, 78).
What charts did Waldseemüller have for guidance? This question cannot be answered with certainty. No marine charts showing the Americas as Waldseemüller does have survived. These portolan charts would have been Portuguese or Spanish in origin, and these were supposed be kept secret, but copies were made of them.
Influential Portolans: Nicolo Caveri • Juan de la Cosa • 1502 Cantino
The chart of Nicolo Caveri (Canerio), made about 1505 in Genoa, could have been used for the depiction of the Americas. The Caveri is a large manuscript map on vellum, made in ten sections. The center of the map is placed in Africa. From the center two circles are drawn with divisions and connecting lines that form the grid of the map (see portolan chart commentary). However, the Red Sea on this chart is oriented almost east-to-west, while the Waldseemüller map shows it with a strong north-to-south orientation. Also, India shown on the Caveri map has a nearly correct shape, while it is truncated on the Waldseemüller map.
As Waldseemüller wrote: ". . .we have not followed Ptolemy in every respect, particularly as regards the new lands, where on the marine charts we observe that the equator is placed otherwise than Ptolemy represented it" (Waldseemüller 1907, 78). What charts did Waldseemüller have for guidance? Besides the Caveri, the Juan de la Cosa map of ca. 1500, made by the Basque pilot who sailed with Columbus, is another possibility, as is the anonymous portolan chart of 1502 that is called the Cantino map because it was smuggled out of Portugal by Alberto Cantino, an envoy of the Duke of Ferrara. It was used by Italian and German mapmakers. The Cantino map, like the Caveri, is made in the form of a nautical chart. Because the geography of Africa, India and the East are much superior on both the Caveri and the Cantino than they are on either of Waldseemüller's maps of 1507, it seems possible that the "marine charts" used by Waldseemüller were of the Atlantic lands and seas only.