Voremonger
Warlord
In any case, I think the current Tourism system has two important properties that are not obvious:
- It mostly reduces the effective Tourism of somewhat large empires, but not of very large empires. Somewhat large empires with ~10-15 Cities are hit sharply by the Tourism modifier. However, the minimum Tourism modifier you can get for your Cities is 25%. Because of this there is a point where each new City is beneficial for your empire-wide Tourism. For the proposed reduction of 5% per City this is 16 Cities. After this point your Tourism modifier stays constant. I have attached a plot for the effective Tourism output of an empire if every City were to produce 1 Tourism per turn. Note the linear increase for very large empires. Also note that a constant amount of Tourism per City is not realistic until very late in the game.
- The Tourism modifier from the number of Cities stacks additively with the modifiers from Technologies. The late game is the most important phase for a Culture victory since this is when the output of Culture/Tourism is the highest. However, this is also the phase in which the Tourism modifier from the number of Cities matters the least because it is mitigated by Technologies. I don't remember the exact numbers but after I researched The Internet I had like +35% Tourism in all of my ~30 Cities. Printing Press gives you +15% Tourism I think so that alone boosts the empire-wide Tourism output of very large empires by 60%.