The Earth. Basic knowledge of the earth's geography survived the economic decline of the Western Roman Empire in the quadrivial subjects of astronomy and geometry, which delineated the climatic zones on the spherical earth. The classical Greek division of the habitable world into the three continents of Asia, Africa, and Europe, surrounded by ocean, is evident in the earliest medieval maps, and knowledge of the earth's sphericity was evident among the Vikings, who had been successfully navigating westward to Greenland and Nova Scotia by following fixed latitudes. However, efforts to map both land and sea in a way that represented real distances and relations between places did not happen until the mathematical methods of the ancient scholar Ptolemy were rediscovered and used in conjunction with compass and triangulation during the Renaissance.

Portolan and Compass. Europeans became aware of the directional properties...