The growth of the urban component of a nation and the shift in population from rural to urban areas in the course of industrial development are processes that show both regularity and predictability. Consequently, it is possible to describe the concentration of population in terms of population density and area by comparatively simple expressions. In this paper expressions are examined for the distribution of people within cities, for the distribution of city sizes within the United States, and for the total population contained within boundaries described in various ways. These generalizations have many applications, both in industrial planning and in civil defense and other military considerations. The paper shows how it is possible to make approximate estimates of the total population serviced by operations of specified types as a function of the cost structure of the operation.