Cosmography and sources

Andrea Bianco (active ca. 1430-ca. 1464), cartographer and Venetian naval official, was one of the collaborators of Fra Mauro (active ca. 1430-ca. 1459/1464) in the creation of the world map commissioned by the court of Portugal’s King Afonso V (1432-1481) in 1457. Earlier work by Bianco that still exists today consists of a small nautical atlas he designed and signed in Venice, 1436, and a nautical chart, signed in London, 1448.

The nautical atlas measures 28 x 36 centimeters (11 x 14 inches), and contains seven nautical charts representing the Mediterranean basin, North Africa, and northern Europe, along with a round world map, a Ptolemaic planisphere, and an explanation of the so-called “toleta de marteloio”, a trigonometric table used with a compass to calculate navigation routes. In this work Bianco brings together all the diverse languages available in the first half of the 15th century for the graphic representation of geographic space.

The nautical chart made in London measures 63 x 85.5 centimeters (roughly 25 x 33.6 inches) and displays in an innovative manner the western coasts of Africa as far as Cape Verde in Senegal and Kabrousse, between Senegal and Guinea-Bissau. The inclusion of these last details demonstrates that the map was up to date according to the 1444 and 1446 explorations of the African coast by Portuguese navigator Aires Gomes da Silva y Fernandes.

Alongside the contemporaneous world maps by Albertin di Virga (active 1387-1419) and Giovanni Leardo (active 1442-1453), Bianco’s nautical chart and atlas exemplify the types of cartographic resources available to Fra Mauro. A comparison among them is quite useful in helping to comprehend what made Fra Mauro’s map so exceptional. Simply in terms of size, Fra Mauro’s map is almost 6 times larger than the total area of the nautical charts forming Bianco’s atlas. It is 7 times larger than Bianco’s London chart, and nearly 20 times larger than Leardo’s most sizeable world map, dated 1452, with a diameter of almost 40 centimeters (15.7 inches).