heres the rules for cities,
Cities: Cities are the main focus of the game, in Cities your people live, work, and grow in population. Cities are built by Settlers. Your cities produce gold, which in turn lets you buy units buildings, and wonders. By taking all of a nations cities and settlers you parylize that Civ.
cities come in 3 sizes: town, city, metropolis
-town; 1-4 citizens
-City; 5-9 citizens, 10% defensive bonus
-Metro; 10- citizens, 25% defensive bonus
Citizens: your first city starts out with 2 citizens, you can use 2 citizens to build a settler. 1 citizen provides you with 5 gpt. you gain 1 citizen each turn, but this process can be sped up (see granaries), you might also lose citizens in artillery strikes and air raids. citizens may become unhappy after the population limit reaches five, they might also suffer from war weariness. they also might want regime change and will protest (for more info see government). when this happens you can make a citizen an entertainer, that citizen no longer produces gold. Certain buildings increase happiness.