This Portolan Atlas of the Mediterranean consists of 8 pages, of which 7 are nautical charts of the Mediterranean Sea and the countries surrounding it and the other is an astronomical calendar.
This sheet features the Iberian Peninsula with part of Corsica, Sardinia, and the North African coast. Homem depicts the Pyrenees in blue a short distance away from their actual location and the Sierra Nevada in a pinkish color. The map also includes oversized depictions of the mouths of the Rivers Tajo and Guadalquivir to prove they could be navigated by boat. The flag of Portugal and coat of arms of Castile and Aragon (without the lions of Castile) also appear.
Diogo Homem was a Portuguese cartographer and the son of royal cartographer Lopo Homem. He worked in Lisbon, London, and Venice, although most of his time was spent in the latter.
Medieval "portolans" (also called "portolan charts") were cartographic instruments that, together with other nautical equipment such as compasses, became indispensable tools allowing ships to move safely around the Mediterranean coastline. Their origins can be traced back to the "peripli" manuscripts used to record oral descriptions of coastal routes by Greek and Roman navigators. In time these developed into "portolan charts": a geographical summary including port characteristics, approximate distances between coastal features, river mouths, anchorage information, and any other references that a seafarer might find useful on their journey. This information was written on parchment or a similar material, resulting in what are now known as nautical or portolan charts.
Portolan charts were first created in the Middle Ages (13th century) and were produced until the Early Modern Period. They were originally made in a region of the Mediterranean where there were intensive political, commercial, and cultural links between cities. Major centers of map production included Majorca, Genoa, and Venice.