This map is actually the Hereford Mappa Mundi.
Produced around A.D. 1300, it is the oldest surviving medieval
map from England and "the largest, most detailed and
most perfectly preserved medieval map in the world" (Peter
Whitfield, The Image of the World: 20 Centuries of World Maps,
San Francisco: Pomegranate Artbooks, 1994, p. 20).