Housing needs a certain amount of culture/science points to evolve to a better state. For example, a shack needs to get 15 culture points to evolve into a hovel.
The exact number of points needed for each housing level can be seen in the Housing Model Data.
The following table shows all the culture and science buildings, their walkers and the points the walker gives when he passes a house.
|Stadium Bonus (Citywide)||10|
|Museum Bonus (Citywide)||10|
Now how can you use this data to your advantage? Let's do an example:
You want townhouses in your Greek city, they need 45 culture points, and you are tight on space and/or money.
If you look at this table, you see that you can build a college + podium for 15 points, a gymnasium for 20 points. If you have a working stadium in your city, that'll get you another 10 points, regardless of whether a competitor goes past your houses or not.
Together, that's 45 points, so there's no need for that big theater in your townhouse blocks!