Within the limitations prescribed, however, the inevitable processes of human nature proceed to give these regions and these buildings a character which it is less easy to control. Under our system of individual ownership, for instance, it is not possible to determine in advance the extent of concentration of population in any given area. The city cannot fix land values, and we leave to private enterprise, for the most part, the task of determining the city's limits and the location of its residential and industrial districts. Personal tastes and convenience, vocational and economic interests, infallibly tend to segregate and thus to classify the populations of great cities. In this way the city acquires an organization which is neither designed nor controlled. Physical geography, natural advantages, and the means of transportation determine in advance the general outlines of the urban plan. As the city increases in population, the subtler influences of sympathy, rivalry, and economic necessity tend to control the distribution of population. Business and manufacturing seek advantageous locations and draw around them a certain portion of the population. There spring up fashionable residence quarters from which the poorer classes are excluded because of the increased value of the land. Then there grow up slums which are inhabited by great numbers of the poorer classes who are unable to defend themselves from association with the derelict and vicious. In the course of time every section and quarter of the city takes on something of the character and qualities of its inhabitants. Each separate part of the city is inevitably stained with the peculiar sentiments of its population. The effect of this is to convert what was at first a mere geographical expression into a neighborhood, that is to say, a locality with sentiments, traditions, and a history of its own. Within this neighborhood the continuity of the historical processes is somehow maintained. The past imposes itself upon the present and the life of every locality moves on with a certain momentum of its own, more or less independent of the larger circle of life and interests about it. In the city environment the neighborhood tends to lose much of the significance which it possessed in simpler and more primitive forms of society. The easy means of communication and of transportation, which enables individuals to distribute their attention and to live at the same time in several different worlds, tends to destroy the permanency and intimacy of the neighborhood. Further than that, where individuals of the same race or of the same vocation live together in segregated groups, neighborhood sentiment tends to fuse together with racial antagonisms and class interests.