to a Research Project Ernest W. Burgess Abstract The aggregation of urban population has been described by Bucher and Weber. A soc- logical study of the growth of the city, however, is concerned with the de nition and description of processes, as those of (a) expansion, (b) metabolism, and (c) mobility. The typical tendency of urban growth is the expansion radially from its central business district by a series of concentric circles, as (a) the central business district, (b) a zone of deterioration, (c) a zone of workingmen s homes, (d)a residential area, and (e) a commuters zone. Urban...