Another element that suggested danger and thus contributed to the heroic narrative was the limited geographical knowledge available in contemporary maps and charts. Columbus could argue that he had in fact landed off the coast of Asia because the maps and charts of the time provided very limited assistance. Sea charts had been available since at least the thirteenth century, but for the explorers in the fifteenth and sixteenth centuries headed across the Atlantic, they were especially unreliable and often conjectural and could not give the necessary information about strong and dangerous currents, shoals and reefs to avoid, or the locations of safe harbors.

The harrowing experiences of Juan Rodriguez Cabrillo charting the coast of California and Ferdinand Magellan searching for a strait through South America testify to the hazards of sailing in uncharted waters. As the log of the Cabrillo...