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Influence of portolan charts

At the same time that scholars were consulting maps based on the works of ancient writers, mariners in Europe had developed a tradition of map-making based upon pilots' books of sailing directions, known as portolani. Portolan charts date from the thirteenth century, and began to appear at the same time the magnetic compass was adopted as a standard navigational tool. The characteristic features of portolan charts were detailed drawings of shore lines and the presence of one or more compass roses from which radiated directional lines, known as rhumb lines.

Pilots used these maps for navigation by finding the rhumb line most nearly parallel to their line of travel, and then tracing the line back to the compass rose to find the proper bearing. Compass roses and rhumb lines became a common feature of maps when they began to be printed commercially. The example shown is from an early seventeenth-century map showing the coast of Chile, produced by the Dutch cartographer Henricus Hondius (1597-1651).

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