Urban Economics has a long history of dealing with spatially differentiated markets, where consumers face their choice of both quality and quantity. Although there have been both theoretical and empirical researches, the general aspects of the problem have not been investigated. The aim of this note is to propose a general framework of dealing with the consumer's choice of quality and quantity. We apply our approach to housing markets to propose a residential equilibrium model, in which the equilibrium rent function emerges from the interaction between the supplier and demander of the housing lots. A simple comparative analysis is carried to investigate the impacts of increases in population on the gradient of the housing rent and land price.