Re: Up or down? North or South?

The answer is a historical one. The representation of planets with North up
is based on the common orientation of flat earth maps with North up. The
next question then becomes, why do we orient maps with north up?  

Early maps were mainly used for navigation of the waters around the
Mediterranean, the Atlantic, and around the Southern tip of Africa. To
assists in knowing one's course, a sailor used both celestial navigation
and the compass to give a fixed directional reference.  As you know, a
compass is just a suspended magnet that aligns with the earth's magnetic
field. So, a compass could point either south or north.  North was
preferred because for one thing, it also coincided with the celestial
reference star Polaris, the north star.  Polaris happens to be only 3/4 of
a degree off from true celestial north, the point in the northern sky that
does not appear to rotate with the daily rotation of the earth.  Polaris
was relatively easy to find for sailors because it is in the constellation
Ursa Minor a.k.a. the Little Dipper.  Polaris is also easy to find because
two relatively bright stars in Ursa Major, a.k.a. the Big Dipper, line up
with Polaris almost exactly, making these two stars known as the "Pointer
Stars".  Polaris was also useful for navigation because its angle to the
horizon would tell a sailor his lattitude.  There was no relatively bright
star in the southern sky that is close enough to celestial south to be a
useful navigational reference. 

Also, since most early navigation and celestial observation began with
Europeans, it is likely that there was a certain bias to using the north
over the south.

Incidentally, before the use of compasses and celestial navigation caused
"north up" to be the standard convention, the first maps were drawn with
east up, out of deference to the Holy Land, which for most Europeans was to
the east.  Turning a map so that east was up was termed "orientating" a
map, i.e. turning it to the "orient," meaning east, which is where we get
the word "orientation."