What determines what culture a settlement is?

[Align]

At first I thought it was the most recent or highest level colony, but I just took over Byzantium as Parthia and got massive unrest from Western Civilized Culture, despite not having built any colony yet. In fact I'm not sure I'll be able to hold on to it long enough to build one...
Moreover, just north is Tomi, which despite me having completed a Persian colony is still considered a Barbarian culture city. It's got both native nomad and native Getic cultures, as well as a Hellenic Emporia in it, so what's going on?

[GeoHitmanGR]

At first I thought it was the most recent or highest level colony, but I just took over Byzantium as Parthia and got massive unrest from Western Civilized Culture, despite not having built any colony yet. In fact I'm not sure I'll be able to hold on to it long enough to build one...
Moreover, just north is Tomi, which despite me having completed a Persian colony is still considered a Barbarian culture city. It's got both native nomad and native Getic cultures, as well as a Hellenic Emporia in it, so what's going on?

Hi. A settlement's culture is determined by the highest combined total of cultural influence from buildings (And only buildings, not people or neighbouring regions).

Already present colonies generate reduced influence if the occupying faction is not of that culture while present natives always generate full, and if there are a lot of them combined, it's possible to still generate more cultural influence than a standard lvl1 colony of the faction's culture.

It may sound a bit complicated but it's a piece of cake once you get the hang of it.

EDIT: A more hands on example may help. In the case of Tomi, it should have
40-55% total barbarian influence (25% from getic natives + 15% from nomad natives + a possible 5% from a barbarian tavern if exists + a possible 10% from a reduced barbarian colony if exist)
10-15% total western influence (10% from the reduced greek colony + a possible 5% from an odeon if exists
40-50% total eastern influence (40% from unreduced persian colony + a possible 5% from public garden if exists + a possible 5% from regional pacificaton if exists)

So it's entirely possible fot tomi to be still barbarian, or even unconvertable if someone managed to constuct a barbarian colony atop all of them. i'd suggest destroying the tavern if exists and upgrading military occupation to regional pacification.

[Align]

That fits what I saw at Tomi, but Byzantium was a mystery - it had no Eastern Civilized influences apart from one of the neighbouring regions. Unfortunately I don't have the save so I can't take a picture or anything...
Now that I think about it though, it had about equal amounts of Barbarian and Western influence from buildings now that it was under my control (rather than the Macedonians who'd get much more Western influence, hence the 95% from that source). Maybe it was actually Barbarian cultured? I'd get the huge public order penalty then too. Mystery solved, probably.

[GeoHitmanGR]

Glad to be of help. IIRC, just a final note, in case of cultural tie the settlement assumes the culture of its governor (Only if it breaks the tie), or finally the culture of the Faction leader (if a governor does not exist or fails to break the tie, for example an eastern governor in a settlement with a cultural tie between barbarian and western).

[Wolf Priest]

Roman colony + Government = 30%
Illyrian natives + Germano-Gallic colony = 30%
So why is Segestica barbarian then, if both my FL and FM governing are Western?