Portolan Chart of Western Europe Showing the British Isles(001ADD000018154U00007000)
This is a portolan chart from a bound atlas dating from around 1540. It is the work of Battista Agnese, a chart maker from Genoa, who prepared many portolan Atlases in the 16th century. Invented by mariners, portolan charts take their name from the Italian ‘Portolano’, meaning a written description of Catalan and Italian ports along a coastline. The first portolan Charts date from the late 13th century and represent an important change in the use of maps and charts. Until this point, most maps had held a religious significance and purpose, such as the medieval mappa mundi which was based on theological beliefs. The portolan chart contrasts with this tradition as they are based on direct observation and first hand experience and have a practical purpose. Reflecting their use by sailors they note only coastal locations, omitting most of the internal detail of the land. Place names are written at right angels to the coast, the more important ports in red ink. The lines which cover this and all other portolan charts are lines of constant bearing known as rhumb lines. These radiate from compass roses and allow the sailor to plot a course from harbour to harbour using dividers and straight edge. Here Scotland is presented as an island separated from England by a tract of sea. The Welsh coast line does not include the Bay of Cardigan a feature that was first accurately depicted in printed form by Gerard Mercator in 1564. Ireland is shown here with the fabled Purgatory of St Patrick. This was a legendary internal lake populated by over 300 tiny islands. Its inclusion in many portolan charts reveals how little was known about the geography of Ireland and how much chart makers borrowed from one another.