There is no top of the map since there is no objective frame of reference in space. The axis on which the Earth spins relative to its orbit is a point of orientation but which side is the "top" is arbitrary.
Sure, but at the end of the day you've got to pick a frame of reference and people have settled on North being the 'top'. You can draw a map that ignores this convention and still have it be valid but you're going to confuse a lot of people.
For what it's worth there's more landmass and population in the Northern Hemisphere so make of that what you will.
