Comparing the data provided by Ptolemy (ca. 100-ca. 178) with the far more accurate measurements given on medieval nautical charts and with the travel accounts of merchants and missionaries, Fra Mauro (active ca. 1430-ca. 1459/1464) reduced the longitudinal extension of the inhabited world to 130 degrees, a conclusion slightly less than the approximately 140 degrees that actually separate the western coasts of Africa from the eastern coasts of China.
The same geographic extension is attributed in latitude, as Fra Mauro adds approximately 30 degrees to the north and 20 degrees to the south with respect to the coordinates indicated by Ptolemy. In latitude, the world of Fra Mauro thus extends approximately 5 degrees beyond the North Pole, with an extension of roughly 35 degrees of latitude to the south.