North

The notion that north should always be up and east at the right was established by the Egyptian astronomer Ptolemy (90-168 AD). "Perhaps this was because the better-known places in his world were in the northern hemisphere, and on a flat map these were most convenient for study if they were in the upper right-hand corner," historian Daniel Boorstin opines. Mapmakers haven't always followed Ptolemy; during the Middle Ages, Boorstin notes, maps often had east on top--whence the expression "to orient."