I discussed it as follows before it passed at Christie's in London on November 19, 2014 :
The Mediterranea is a coveted sea but the Ottoman domination pushes the Western trade outside it. The time has come to travel the coast of Africa to seek new paths to the Orient. Portugal is geographically well positioned for this new exploration. The age of the great discoveries is starting.
Navigation at sea is dangerous. Portolans are used to transmit the knowledge of the seafarers. These charts provide some major advantage over enemy ships and are considered as highly strategic.
The portolan is not a map in the modern geographic meaning. It is a document that sets islands and coasts and identifies the ports. The sailors are guided by the lines of the compass rose from focal points mostly in sixteen wind directions.
Christie's sells a manuscript on vellum of a portolan atlas of the coasts of Atlantic and North Sea, consisting of seven double-page 39 x 50 cm charts in a Venetian backless binding of the period.
The view of the coasts is complete from Sierra Leone and Guinea in the South to Jutland and Scotland in the North. It includes the discoveries made in the coast of Africa by Cadamosto, a Venetian serving the Portuguese, and by Pedro de Sintra in 1460.
One page is signed, located and dated : Gratiosus Benincasa Anchonitani, Venice, 1468. The Benincasa portolan anticipates by thirteen years the first Portuguese mission of African circumnavigation. Benincasa is one of the best cartographers of his time and his work in the Mediterranea are among the sources used to compile the Cornaro atlas in Venice around 1489.