There is no generally accepted comprehensive definition of a portolan chart. Given that the production extended over four hundred years in many different cities for different clients with different purposes, perhaps this is not surprising.
A particularly significant portolan chart of this period of Portuguese exploration of the West African coast is found in an anonymous atlas now preserved in the British Museum (Egerton Collection, ms 73).
Campbell, Tony (1987) "Portolan charts
from the late thirteenth century to 1500", Chap.
The essays that specifically stand out exploring this transfer are Jonathan M Bloom's 'Lost in Translation: Gridded Plans and Maps along the Silk Road,' Dickran Kouymjian's 'The Intrusion of East Asian Imagery in Thirteenth-century Armenia: Political and Cultural Exchange along the Silk Road' and Sonja Brentjes's 'Revisiting Catalan Portolan Charts
: Do they contain Elements of Asian Provenance?'
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.
Chapter 2 'Landmarks of Mapping' provides historic context with the usual references to Mappae Mundi, portolan charts
and so on, as well as maps from the ancient worlds.
It appears that one of his primary sources on these manuscript sea charts (portolan charts) is Periplus by Baron Adolf Erik Nordenskiold, published in 1897.
And when discussing attempts to adapt the technology of portolan charts to the open oceans, he confuses the function of the oblique meridians found in extreme northern latitudes on some charts as providing a correction of scale, when in fact these oblique meridians were a (misguided) effort to correct for direction in these latitudes.
Such "transitional" maps blended components of Portolan charts, Ptolemy's Geographia, and biblical themes.
The section also includes portolan charts and other elaborate manuscript maps.