Just as the city as a whole is influenced in its position, function, and growth by competitive factors which are not the result of the design of anyone, so the city has an internal organization which may be termed an ecological organization, by which we mean the spatial distribution of population and institutions and the temporal sequence of structure and function following from the operation of selective, distributive, and competitive forces tending to produce typical results wherever they are at work. Every city tends to take on a structural and functional pattern determined by the ecological factors that are operative. The internal ecological organization of a city permits of more intensive study and accurate analysis than the ecology of the city from the external standpoint. For the latter phase of the subject we will have to rely on further investigations of the economists, the geographers, and the statisticians. The facts of the local groupings of the population that arise as a result of ecological factors are, however, readily accessible to the sociologist. I. Plant ecologists have been accustomed to use the expression “natural area” to refer to well-defined spatial units having their own peculiar characteristics. In human ecology the term “natural area” is just as applicable to groupings according to selective and cultural characteristics. Land values are an important index to the boundaries of these local areas. Streets, rivers, railroad properties, street-car lines, and other distinctive marks or barriers tend to serve as dividing lines between the natural areas within the city. Addams, Jane. _A New Conscience and an Ancient Evil_ (New York, 1912). A discussion of vice and the vice district in Chicago. (V, 4; VI, 6.) Anderson, Nels. _The Hobo: The Sociology of the Homeless Man_ (Chicago, 1923). The study of a typical deteriorated area in the city where the homeless men congregate. (VII, 5; IX, 4.) Bab, Julius. _Die Berliner Bohème_, Vol. II in “Grossstadt Dokumente” (Berlin, 1905). An intimate study of a natural area which has developed an exotic atmosphere as a result of the social isolation of its members and their peculiar personalities. At the same time furnishes an excellent history of a local community and is a unique contribution to the mentality of city life. (V, 3; VII, 2; IX, 2, 3, 4.) Booth, Charles. _Life and Labor of the People of London_ (London, 1892). The most comprehensive study of London in existence. Especially interesting in this connection for its description of the natural areas of that city. Volume V, on East London, offers a wealth of insight into city life. These volumes cover almost every phase of city life and should be cross-referenced with most of the categories suggested in this outline. Brown, Junius Henri. _The Great Metropolis: A mirror of New York_ (Hartford, 1869).