Portolano

A portolano or rhumb chart (also compass chart, ruttier book) is a medieval nautical map (for coastal navigation) on which lines are drawn from a point at the centre to the directions of the compass or the winds. By the 17th century, rhumb charts were an indispensable part of navigators' handbooks (portolani). Providing in continuous sequence detailed descriptions of coasts, they were an important navigational aid.