Portolan chart

Portolan charts are navigational maps based on realistic descriptions of harbors and coasts. They were first made in the 1300s in Italy and Spain. The word portolan comes from the Italian adjective portolano, meaning "related to ports or harbours." These charts, actually rough maps, were based on accounts of medieval Europeans who sailed the Mediterranean and Black Sea coasts. Frequently drawn on sheepskin, portolan charts show coastal features and ports.

The straight lines criss-crossing many portolan charts represent the thirty-two directions (or headings) of the mariner's compass from a given point. This is similar to the compass rose displayed on later maps and charts. Naming or demonstrating all thirty-two points is called boxing the compass.

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. In addition, the charts offered a realistic depiction of the shore, and they were meant for practical use by a mariner of the period.

The portolan failed to take into account the curvature of the earth; so, they were unhelpful in crossing open ocean. Portolani were useful for navigation in smaller bodies of water, such as the Mediterranean, Black, or Red Seas.

The oldest extant portolan is the Carte Pisane dating from approximately 1296. The cartographer, Angelino Dulcert, produced a portolan in 1339.