We pretty much take it for granted that, when we spread a map out on a table, the top of the paper is going to be north. But if you think about it, there’s no absolute reason that should be the case. In fact, ancient Egyptian cartographers positioned south at the top of world, possibly because of the south-to-north flow of the Nile River. During the Middle Ages, map-makers based their work on both the rising of the sun and Christian symbolism to place east at the top of the map. This dominance of the east is why, today, we talk about using a map to “orient” ourselves. But our modern, north-focused perspective ultimately goes all the way back to Ptolemy, from second century Egypt, whose beautifully detailed charts of the known world, complete with latitude and longitude reflecting the curvature of the earth, placed north at the top. It is unknown why he chose this layout, but his work was so influential on mapmakers throughout the centuries that followed, that he literally changed the way we view the world today.