Abstract This paper contains a description of a general class of city formation models. Individual economic agents have preferences for locations that depend upon the population distribution. A location's attractiveness depends upon some combination of its population and its average distance to other agents. Economic variables enter indirectly. Taking this broad perspective leads to a deeper understanding of how cities form as well as of the sensitivity to initial conditions of their locations and sizes. In addition, this class of models supports scenarios where cities emerge: without any assumptions that agents wish to live near or with one another, agents cluster into cities.