THE income of the various districts within a metropolitan area cannot be computed from sources (such as manufacturing, mining, agriculture, wholesaling, retailing, etc.) for the reason that many people do not live in the districts where they work. Income must be computed for the families living in the various parts or districts in the area. This can be done from Census figures showing rents paid and value of homes owned by the occupants. A method of doing this and measuring the flow of retail trade within the area has been suggested previously.2 Here we show application of this method using the Chicago Metropolitan Area as an example. The Census gives retail sales figures only for political divisions. Hence this method will not show the movement of trade within a city. When a metropolitan area consists of several political subdivisions, the movement of trade between these subdivisions can be computed. This movement is important to the merchants in the districts involved, to students of marketing, and to manufacturers and wholesalers selling in the area. If the Census in the future publishes sales figures for districts within a city, it will then be possible to use the method outlined here in measuring the movement of trade between districts or sections within a city. The method consists of three steps: 1. Computation of incomes of the various