Citizens are an obvious reference to the Sims by the interactions they play out. Along with keeping them happy(Unhappy citizens might make an uprising on the space stage), if you observe them long enough, you can see them do various activies, such as military drills, mass praying, protests and even weddings(Though, that takes a very long time). They may also have minor activities, such as looking through telescopes, boxing, pushups, and sometimes you can see them doing magic tricks for others to watch. If the city is military, they fight and train and fire guns when they aren't doing anything. If the city is religious, they pray, sing and do strange rituals when other citizens die. If the city is economic, they will do money-based activities, such as money giveaways and doing a roullete game.
Main article: Civilization Stage