Portolan chart

Portolan charts are the earliest known type of nautical charts, and the oldest known examples were made in the late 13th and early 14th centuries in the Mediterranean region, usually displaying the areas between the Atlantic coasts of Western Europe and Northwestern Africa to the west and the Black Sea to the east. Besides those showing the entire area on a single map field, there are also portolan charts that show smaller territorial extents, either as separate editions or as a series of charts that together form portolan atlases.

The word portolan comes from the Italian portolano, meaning "related to ports or harbors", and which since at least the 17th century designates "a collection of sailing directions".

Portolan charts are manuscript charts rendered using ink on vellum sheets and are easily recognizable by their distinct visual characteristics, such as a content focus on coastal regions, networks of colour-coded straight lines emanating from one or more centres in 32 directions, linear scale bars calibrated in so-called portolan miles (miglio), and place names inscribed perpendicular to the coastline contours. Their most perplexing features are the extremely realistic portrayal of coastlines and a complete historical lack of their evolutionary path because the oldest known samples have already been made to a highly developed stage, and later-made charts and atlases have not become more accurate over time.