This talk is concerned with issues related to social diversity in urban environments. We introduce a model of real estate transactions between agents which are heterogeneous in their willingness to pay. A key feature of the model is the assumption that agents preferences for a location depend both on an intrinsic attractiveness of the location, and on the social characteristics of its neighborhood. Focusing on the case of a monocentric city, the stationary state is analytically characterized and gives the distribution of income over space. The model is studied through numerical simulations as well