Illarion Snowe was known as the tyrant of the north but the territory was actually not due north when considering New Albion as a whole. It was neighbors to Basilea, hugging the coastline, with a mountain range between. A more north-westerly direction than anything else.
Marquess Snowe and the nobles that were his vassals were called "the northern nobles" mostly due to two reasons.
First, it had to do with the name of the territory. Illarion Snowe was the Marquess of Norden.
The other reason primarily had to do with historical significance. It was similar to the Basilea Duchy, in that it had been its own sovereignty, only they chose war. New Albion fought with the "North" for a long time, a land of savages and supernatural beings, until a calamity struck Norden and a civil war broke out.
Some prominent figures resorted to allying with New Albion, the most significant being a Snowe ancestor, submitting to the Morgaine family in exchange for support.