Such "transitional" maps blended components of Portolan charts
, Ptolemy's Geographia, and biblical themes.
Blake relates the development of the sea chart from the days when manuscripts were drawn on sheep skins, such as the portolan charts
that survived from the thirteenth century, through the maritime ascendancy of the Spanish and Portuguese, then the Dutch, French, and British through the eighteenth century, when the discovery and charting of the coasts and the oceans of the globe had become a strategic naval and commercial requirement, to the modern Admiralty charts of today.
In the last part, 'The Mediterranean Road,' Paul Kunitzsch presents the tools of premodern Arabic-Islamic astronomers such as three-dimensional celestial globes and the astrolabe, and finally Sonja Brentjes states that elements in fourteenth-century Catalan portolan charts
are similar to the late Ilkhanid school.
The second section also covers the contributions of one of the most important cartographers, Claudius Ptolemy, while the third examines three distinctive types of Medieval European maps, mappaemundi (a Latin term meaning maps of the world), Portolan charts
(ship's pilot charts that show sailing directions and ports), and regional maps.
His most brilliant ideas--which should have been more fully developed--unify the symbolism and structural elements of portolan charts
within a general discussion of central and peripheral space.