In EU2, a building represents many features of settlements. On the city screen, you can see both buildings and potential building sites for city improvements which are not yet constructed. Most buildings can be clicked, with effects varying depending on the building. City upgrades are the most important subcategory of buildings, since the player controls whether or not they are built. Thus they involve strategy. Clicking on a nonbuilt city improvement always gives you a dialog to choose whether to build it. Once they are built, city upgrades do nothing when clicked on.