_Ecological forces._—The ecological forces are those which have to do with the process of competition and the consequent distribution and segregation by residence and occupation. Through competition and the factors which affect it, as trade centers, etc., every neighborhood in the city becomes a component and integral part of the larger community, with a destiny bound up by its relation to it. In the study of the growth of the city it is found that the life of any neighborhood is determined, in the long run, not altogether by the forces within itself, but even more by the total course of city life. To think of the neighborhood or the community in isolation from the city is to disregard the biggest fact about the neighborhood. Studies of urban growth reveal that the city grows outward from its central business district (1) in a series of expanding zones.[73] There is a “zone of transition” (2) encircling the downtown area. This is the area of deterioration, the so-called “slum”, created in large part by the invasion of business and light manufacture. A third area (3) is inhabited by workers in industry who have escaped from the area of deterioration (2) and who desire to live within easy access of their work. Beyond this zone is the “residential area” (4) of high-class apartment buildings or of exclusive “restricted” districts of single family dwellings. Still farther, out beyond the city limits, is the “commuters’ zone” (5) of suburban areas or satellite cities within a sixty-minute ride of the central business district. Within these zones of urban growth are to be found local districts or communities, and these in turn subdivide into smaller areas called neighborhoods. In the long run, geographical factors and the process of competition fix the boundaries and the centers of these areas. It is important that neighborhood work be in accordance with, rather than in opposition to, these silent but continuous influences. A map of local communities was prepared to show the way in which rivers, railroads, large industrial establishments, parks, and boulevards divide the city into its constituent local communities—residential and industrial. The centers of local communities are to be found at the point of highest land value in the intersection of two business streets. These local community centers are also characterized by the concentration of retail business, of banks, of restaurants, and of the large and magnificent palaces of amusement, like motion picture houses and public dance halls. If high land values indicate the center of the community, the lowest land values generally define its periphera. [Illustration: CHART I SCHEMATIC REPRESENTATION OF THE DIVISION OF A COMMUNITY INTO NEIGHBORHOODS BY THE INTERSECTION OF TWO BUSINESS STREETS. ]