Portolan chart of Jorge de Aguiar (1492)

Commentary
Portolan chart of Jorge de Aguiar (1492)

Medieval maps with superimposed compass directions are known as ‘portolan maps’ or ‘portolan charts’ (from Italian portolano). They are characterized by their system of rhumb lines, usually emanating from wind roses, as well as their remarkably accurate outlines of the coasts of the Mediterranean and surrounding regions. Portolan typically show no geographical inland detail except for ports and river mouths. They often come with a mile scale that allowed pilots to calculate the distance between any two places depicted on the chart, which together with compass directions provided the basis for dead reckoning.

Commentary. Philipp Nothaft (May-June 2019)