What is "t and o map"

n. (context historical cartography English) A type of mediaeval map of the world, representing only the top half of a spherical Earth.

A T and O map or O-T or T-O map (orbis terrarum, orb or circle of the lands; with the letter T inside an O), is a type of medieval world map, sometimes also called a Beatine map or a Beatus map because one of the earliest known representations of this sort is attributed to Beatus of Liébana, an 8th-century Spanish monk. The map appeared in the prologue to his twelve books of commentaries on the Apocalypse.