The relationship between the level of income and the population of an urban area is a familiar concern in urban economics. Existing models of the relationship between income levels and urban population are considered to assume that there is a homogeneous labor force and, hence, a world in which there is no inequality in the size distribution of income within an urban area. In this paper, a world is modeled in which there are two classes of workers and the relationship between urban population and the distribution of income between these two classes is examined. In particular, it is determined what happens to the degree of inequality in money incomes as urban population increases, if each class of worker is compensated for the higher costs associated with larger urban size. The analysis in this paper is based on a mathematical model of an urban area which allows us to calculate how the income distribution--as measured by a Gini coefficient--changes as urban population changes. This model is solved numerically for a variety of assumptions about the initial size of the urban population and its division between skill classes, initial income distribution, commuting costs, and several other parameters. The findings of the simulations using this model are then tested using data for a sample of metropolitan areas. (Author)