Finite is, obviously enough, another way of saying "limited." That Nirn has "limits" is well attested to. Nirn was puzzled together from pieces that were never supposed to hold together in the first place, so someone had to put up a few fences to keep the neighbors out and the children in.
I don't think it's that obvious at all.
"What are planets?
The planets are the gods and the planes of the gods, which is the same thing. That they appear as spherical heavenly bodies is a visual phenomena caused by mortal mental stress. Since each plane(t) is an infinite mass of infinite size, as yet surrounded by the Void of Oblivion, the mortal eye registers them as bubbles within a space. Planets are magical and impossible. The eight planets correspond to the Eight Divines. They are all present on the Dwarven Orrery, along with the mortal planet, Nirn.
What is Nirn?
Nirn (Ehnofex for 'Arena') is a finite ball of matter and magic made from all of the god planets at the beginning of time, when Lorkhan tricked/convinced/forced the gods to create the mortal plane. Nirn is the mortal plane and the mortal planet, which is the same thing. Its creation upset the cosmic balance; now all souls (especially the Aedra-Daedra/Gods-Demons) have a vested interest in Nirn (especially its starry heart, Tamriel)."
Further, it goes on to refer to moons as small planets. Not once, though, is Nirn called a planet. Rather, the Planets seem to be the finite(to the mortal mind) expressions of infinity. Space is a planet. That which is outside space is a planet. Nirn, however, is just a ball of stuff floating in infinity.
Not an infinity wrapped in infinity, but finity wrapped in infinity.
Ah. You were talking about the difference between concepts and things and using them to explain the difference, these are fundamental properties of the God and Nirn respectively. The appearance of size and distance are merely the impression they create on a mortal mind. In other words, irrelevant.
Irrelevant compared to what? What is relevant?
I have actually. The shape of Nirn is roughly spherical and it's circumference half that of earths, about 20.000 kilometers. This can be derived from the known distance of 250 miles from Red Mountain to the City of Almelexia as described in the PGE and the degrees longitude as written on the Red Gaurd map. Further more, it's highest Point is Red Mountain with 10 kilometers, this is derived from scaling Morrowind up to a 1:1 scale.
Considering these two parameters, Mars has a strong equivalence.
When I said the point that nobody has written about it, I was talking about the point a couple posts up. When Adanorcil said that nobody bothered to write about the size of Nirn.