Around 1300, an important
innovation in
cartography began to take shape in the
Mediterranean world. This was the development of the portolan chart. This new type of
mapmaking coincided with the massive increase in seafaring and exploration of the
Atlantic which began around this period.
Most commonly, these types of charts were created with sailing directions and often included colorful depictions of real as well as fictitious geographical locations. These maps existed before the days of truly accurate surveying work and printed charts, so ships' captains usually kept large vellum manuscript books of them which held very detailed depictions of trade routes between various ports as well as accounts of harbors and the conditions of different types of coastlines.
The earliest examples of portolan charts are of Italian, Catalan and Genoese origin and date from the fourteenth century and were used for approximately 200 years before detailed engraving and better mapmaking rendered them obselete. The name comes from the Italian word portolano from porto, "port" and translating as "pilot book." Sometimes the full Italian spelling is used while referring to it in English.
Photograph:
http://www.princeton.edu/~his291/Jpegs/Portolan.JPG