City upgrades are improvements that may be built in cities. All city upgrades take time to build, which varies with the upgrade. Upon completion of the project, the city will be improved in various ways. There are a number of different upgrades:
- Officials: Tax collectors, Chief judges, and Governors
- Conscription centers
Each upgrade to a city other than fortresses is either present, or absent. Fortresses have degrees: a city can have none, or a fortress with a "level" of 1 through 6.
It is possible for colonies to have upgrades, but no country can build anything in a colony. Any upgraded colony either began the scenario that way, or else was gifted its upgrade via a scripted event.
While a city upgrade is being built, it is called a project. Only one project may be underway at a time in any given city. Colonization and conversion attempts ongoing in a city will prevent you from beginning a project. Colonists can be sent while a project is in progress; missionaries cannot.