His work was mainly cartographical in its aim, and theory was as far as possible excluded.
They can, however, hardly be described as maps, while in age they are surpassed by several cartographical clay tablets discovered in Babylonia.
Of great value for cartographical work is a careful survey, carried out by American engineers (1897-1898), for a continental railway running along the west coast from Mexico to Chile.
The first sufficient explorations for cartographical record were made by John Smith in 1614, and his map was long the basis - particularly in its nomenclature - of later maps.
In 1427, again, with the co-operation of his father King John, he seems to have sent out the royal pilot Diogo de Sevill, followed in 1431 by Goncalo Velho Cabral, to explore the Azores, first mentioned and depicted in a Spanish treatise of 1345 (the Conosrimiento de todos los Reynos) and in an Italian map of 1351 (the Laurentian Portolano, also the first cartographical work to give us the Madeiras with modern names), but probably almost unvisited from that time to the advent of Sevill.
