The Functions of Portolan Maps:
An evaluation of the utility of manuscript nautical cartography from the thirteenth through sixteenth centuries

Abstract

In the thirteenth century, following the expansion of seafaring city-states and kingdoms in the Mediterranean, a new form of cartography emerged, known as portolan charts. These maps, more secular and scientific than earlier cartographic genres, were produced between the thirteenth and seventeenth centuries, primarily in the western Mediterranean. While portolan charts and atlases have been studied since the nineteenth century, they remain enigmatic. One of the most important questions about them has been: ‘what was their function’? Most scholars have argued that they were fundamentally utilitarian maps, used for navigation. This thesis challenges that theory, and proposes that portolan maps were not navigational.

To critically assess the function of portolan maps, the first chapter evaluates their methods of construction, as determined through an analysis of primary sources, and an original archaeological reconstruction of a portolan chart. The second chapter presents seven case studies of charts, atlases, and their makers, to explore the cartographers’ output, the specific functions of their maps, and how they relate to the genre as a whole. The third chapter analyses the contemporary documentary and literary evidence to gain a better understanding of the economic market for portolan maps. The fourth chapter evaluates their functions, in two parts: the first discusses how the maps could have been used on ships, how they changed over time, and investigates the practical utility of their toponymy and hydrography. The second part explores their alternative functions, which were as administrative and encyclopaedic maps, spiritual and scholarly maps, and aesthetic objets d’art.

Although some evidence suggests portolan maps were used at sea, it is largely circumstantial and unspecific. The evaluation of their construction, specific functions, the output of cartographers, and their practical utility, instead indicates that portolan maps were not navigationally useful, but embodied number of other purposes.