Map of the Unknowable World

It is not surprising that St. Brendan's Isle should be one of the first islands to appear in a medieval mappemundi. It would soon be follwoed by a host of equally legendary islands that gradually filled the previously empty spaces of Oceanus. St. Brendan's Isle was prominently displayed in maps of th etime because the mappemundi were meant to illustrate biblical geosophy rather than provide precise locations or directions. Medieval measures were impreceise and numbers were used for their symbolic rather than their quantitative value. In Brendan's voyages, it takes forty days to reacy virtually every location ... Like the medieval paintings and stories, mappemundi lack a single point of temporal or spatial perspective that owuld allow the viewer to differentiate between the near and far, or between then and now.

-- Gillis, Islands of the Imagination