Interesting question about maps?

Eveytime you look at a map you see all of the northern hemisphere w/ North America, Europe, and Asia. You also see Australia, South America, Africa, and Antarctica below. But my question is why? Why is north always up and south always down on the maps? In the universe there is no up or down so why do we do this? Couldn't the Earth be going around the sun in a vertical rotation (like a bike wheel)