What 1569 map projection became famous for aiding marine navigation?

The 1569 map projection famous for aiding marine navigation was the Mercator projection.

Gerardus Mercator presented it on his large 1569 world map, whose Latin title explicitly described it as adapted for navigators. The projection spreads parallels farther apart toward the poles so that lines of constant compass bearing—called rhumb lines or loxodromes—appear as straight lines. Sailors could plot a steady course more conveniently on a flat chart.

That navigational advantage comes with major distortion. Areas and distances become increasingly exaggerated at high latitudes, and the poles cannot be represented because the scale becomes infinite there. Greenland, for example, appears vastly larger than it is relative to Africa, a feature that has fueled modern criticism of the projection.

Another common misconception is that the 1569 map was immediately adopted by mariners. Although Mercator’s idea was influential, technical limitations and the difficulty of calculating longitude delayed widespread use. The projection became broadly established for nautical charts much later, especially from the late seventeenth and eighteenth centuries. It is useful for direction, not for comparing the true sizes of continents.