From the British Library, an online exhibition: The Unveiling of Britain.

When the ancient Greeks looked beyond their Mediterranean world, Britain was virtually invisible, lost in the mists of legend. Their view, or lack of it, survived as late as the ninth century in maps that do little more than offer a few place names. The Orkneys, for example — the fabled Orcades — are shown unconvincingly situated in the Atlantic just beyond the Straits of Gibraltar. Britain’s shape and contours were gradually uncovered by the world outside, and to some extent by its own inhabitants, during the centuries between 800 and 1600. Through the British Library’s remarkable collection, we can follow the lifting of that veil.

(Thanks, Richard.)