1. A medieval or Renaissance nautical chart or pilot book showing coastlines, ports, and sailing routes, typically with compass roses and rhumb lines.
Usage: historical; nautical; also spelled portolan

Examples

• The explorer consulted a portolano to navigate the Mediterranean coast.
• Medieval merchants relied on portolanos to plan their trading voyages.
• The museum's collection includes several beautifully illustrated portolanos from the 15th century.
• Portolanos were among the most valuable documents for seafarers during the Age of Exploration.
• The portolano showed detailed information about harbors and dangerous reefs along the route.