Why is north up?

Did the early explorers, mapmakers, astronomers, and the like get together and vote, or did it just sort of happen? Does everyone on earth think of north as up, or could a Northern Hemispherian like myself travel south of the equator and buy a globe with Antarctica on top?

The reply:

With a few minor exceptions, which we shall get to directly, mapmakers throughout the world invariably put north on top, even if they were born and raised in Tierra del Fuego. What we are dealing with, in other words, is a case of blatant directionism, the unfairness of which cannot help but rankle any right-thinking person. Why should the big N always be on top when there are hundreds of other directions--thousands, if you get down to seconds of arc--that have an equally legitimate claim on our affections? I grieve to think of the shattered dreams of, say, south southeast.

People who live in the southern hemisphere, notably our friends the Australians, like to give the impression they could care less about how maps are oriented. But don't be deceived. An Aussie friend of mine once showed me a world map printed up by her countrymen that had south on top, thereby putting Australia, as she rather ominously phrased it, "in its rightful place." Mark my words, someday the slogan "Down with Yankee imperialism" will have shocking new meaning.

But getting back to the question. 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." But north prevailed over the long haul. By the time Southern Hemispheroids had become numerically significant enough to bitch, the north-side-up convention was too well established to change.