Portolan Chart

(also portolano), a type of nautical chart used from the 13th to 16th centuries for commercial navigation in the Mediterranean. The coastline was indicated in detail, as were many geographical designations; the inland portions were usually left blank. For determining and plotting a ship’s course, compass grids indicating the position of the points of the compass and sailing directions were drawn at a series of points on the chart; linear scales were also shown, for the first time. In the late 15th and early 16th centuries the portolan chart was replaced by charts with a network of meridians and parallels.