I think if you followed the story of Elder Scrolls you will have a pretty good guess at where the border lines would be but lets see....

http://oyster.ignimgs.com/mediawiki/apis.ign.com/elder-scrolls-online/e/e4/Map_tamriel.jpg
This is a map that has been used a few times to describe the size of TESO
Where do ya see the Faction lines?

Nice map!

http://aijaa.com/eGXmm3

Here is a detailed map of the factions in TESO.