The city-planning literature contains many instances of comparisons between planned cities and natural cities as well as examples of the effects of the city plan on the actual development of the city, and the opposite phenomenon—the effect of the natural development of the city on the city plan. IV. THE CITY AND ITS HINTERLAND Far from being an arbitrary clustering of people and buildings, the city is the nucleus of a wider zone of activity from which it draws its resources and over which it exerts its influence. The city and its hinterland represent two phases of the same mechanism which may be analyzed from various points of view. 1. Just as Galpin, in his _Social Anatomy of a Rural Community_, was able to determine the limits of the community by means of the area over which its trade routes extend, so the city may be delimited by the extent of its trading area. From the simpler area around it the city gathers the raw materials, part of which are essential to sustain the life of its inhabitants, and another part of which are transformed by the technique of the city population into finished products which flow out again to the surrounding territory, sometimes over a relatively larger expanse than the region of their origin. From another point of view the city sends out its tentacles to the remotest corners of the world to gather those sources of supply which are not available in the immediate vicinity, only to retail them to its own population and the rural region about it. Again, the city might be regarded as the distributor of wealth, an important economic rôle which has become institutionalized in a complex financial system. Chisholm, George G. “The Geographical Relation of the Market to the Seats of Industry,” _Scott. Geog. Mag., April, 1910_. Galpin, C. J. “The Social Anatomy of an Agricultural Community,” Agricultural Experiment Station of the University of Wisconsin, _Research Bulletin 34_ (Madison, Wisconsin, 1915). Deals primarily with trade routes of an agricultural area, but throws considerable light on the urban trade area. (V, 2; X, 2.) Levainville, Jacques. “Caen: Notes sur l’évolution de la fonction urbaine,” _La Vie Urbaine_, V (1923), 223–78. Through its emphasis on the economic functions of the city this study makes clear the significance of the trade areas. Newspapers, business houses, and mail-order houses in particular have published numerous discussions and graphic statements of their circulation or their trade relations with the surrounding territory. Such documents are to be found in numerous specialized trade and commercial journals. In addition there are government reports and publications of chambers of commerce bearing on this question.