I made a globe of Nirn, it includes all the known continents/landmasses mentioned above. I put it all onto a globe on a scale that which I figured was a decent size for Tamriel when compared to the planet. The scale I made Tamriel leaves room for at least another huge continent, if not then a few small ones, and some could argue that I made Tamriel too large (based on the coordinates found on the Redguard map IIRC, which would make Tamriel only http://i73.photobucket.com/albums/i201/Vality7/adan_globe.jpg big), which would leave even more room for more land.
You can find my pictures and the video here: http://vality7.googlepages.com/planetnirn
The video is to show the massive amount of ocean beyond Nirn, and if you think I made Tamriel too large in proportion to the planet, then just imagine that there is even more ocean - of course, the ocean is meant to represent the amount of space for other lands, not that there is really a giant ocean there. A few little things - Atmora possibly looks too close to Tamriel, but a lot of the white up there is cloud, and Pyandonea and stuff further south you can't really see due to the angle, but there's enough room for an Aldmeris and a south pole down there. Akavir of course, I made up, but I think it looks kinda cool, a little incomplete though - none of this is really finished. Pics and video were all taken in Nifskope btw, they probably would've been better if I had rendered them properly.
Akivir is by far larger than any of the other continents from what I can tell.
Really? Far larger than Tamriel even?
The Ice Demons (I can't remeber their naems) invaded from the east, into Morrowind, and the Teseci raided in the west. The Empire also launched an invasion of the Teseci lands from the west too, so the way I see it Akivir would be like Eurasia.
All that there says is that Akavir is to the east of Tamriel, unless you meant to say the the Tsaesci raided Tamriel
from the west.