portolás

Portolás refers to a type of navigational chart used from the late 13th to the 16th centuries, primarily in the Mediterranean and Black Seas. These charts were characterized by their detailed coastlines, rhumb lines, and the depiction of ports and harbors. Unlike later Mercator projections, portolás were not designed for accurate plotting of latitude and longitude over long distances. Instead, they prioritized ease of use for coastal navigation, relying on compass directions and estimated distances.

The origin of the term "portolás" is debated, but it is generally believed to derive from the Italian word "portolano," meaning a collection of sailing directions or a book of ports. These charts were typically drawn on parchment or vellum and were often beautifully illustrated with decorative elements, including coats of arms and compass roses.

Key features of portolán charts include the prominent display of rhumb lines, which are lines radiating from compass roses indicating the cardinal and intercardinal directions. These lines helped mariners plot their course by dead reckoning. The coasts were rendered with remarkable accuracy for their time, with particular attention paid to the shapes of bays, capes, and river mouths. Ports were often marked with symbols, and sometimes included textual descriptions of their facilities or characteristics.

Portolán charts were essential tools for medieval and Renaissance mariners, facilitating trade and exploration within the known world. While their accuracy for celestial navigation was limited, their practical value for inshore sailing and inter-port travel was immense. They represent a significant development in the history of cartography and maritime technology.