Chart of the Potomac River and Eastern Branch from the Sister Islands to Geesboro Point and thence to the Navy Yard Bridge : with the topography of the adjacent country : made in pursuance of a resolution of the Corporation of the City of Washington, approved 26th May 1837 /

The word portolan comes from the Italian adjective portolano, meaning "related to ports or harbors", or "a collection of sailing directions". Portolan charts are maps based on compass directions and estimated distances observed by the pilots at sea. They were first made in the 13th century in Italy, and later in Spain and Portugal where they considered to be state secrets. The English and Dutch found the description of Atlantic and Indian coastlines extremely valuable for their raiding, and later trading, ships. The oldest survived portolan is the Carta Pisana, dating from approximately 1296 and the oldest preserved Majorcan Portolan chart is the one made by Angelino Dulcert who produced a portolan in 1339.