Portolan chart

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A Japanese portolan chart of the Indian Ocean, early 17th century

A portolan (derived from the Latin word portus, port) is an early modern European navigation chart, dating from the thirteenth century or later, in manuscript, usually with rhumb lines, shorelines and place names.

The portolan combined the exact notations of the text of the periplus or pilot book with the decorative illustrations of the conceptual T and O map, but a portolan chart did offer a realistic depiction of the shore and was meant for practical use by a mariner of the period. The portolan did not take into account the curvature of the earth, so it was a misleading document for crossing an ocean. Portolani were useful for navigation in smaller bodies of water such as the Mediterranean or the Red Sea.

The oldest portolan which has survived to our era, the Carte Pisane, dates from circa 1296. The cartographer Angelino Dulcert produced a portolan in 1339.