I've put my question in the title, I don't know exactly when a city is going to revolt and couldn't find anything on it in the civilopedia, as it only says there that "superior culture" can dominate opponents' cities. I've now noticed that I now actually have more culture on the tiles on my opponent's side of the border - it says something like 70 % me, 30 % opponent. However, the affected citiy does not rebel.. Are only the "big steps" (10, 100, 500, 5000... in culture important for cultural domination or does the actual value (also in between such jumping points) also count? Well actually you realise I don't have a clue about this issue - and also have trouble formulating what I want to know
I hope I'll get some answers anyway 

