Portolan charts were primarily of the Mediterranean and Black Sea, but were soon extended to include Europe's Atlantic coast. It is interesting to compare Vesconte's chart with the carte pisane, some 20 years older, which has here no more than an inaccurately sketched outline. The coastal outlines of portolan charts developed in a continuous process of adjustment and improvement. Here it is notable how the coasts regularly followed by Mediterranean ships – Portugal, the Bay of Biscay, the English Channel – are far more accurately drawn than those they seldom visited.