Why do urban models tell only a partial story of how cities are constructed?
Urban models tell only a partial story of how cities are constructed because they are the product of human thought processes that are inherently flawed and that do not -- and cannot -- account for every kind of demographic, social and economic transformation that societies encounter over time.
Especially during the middle of the 20th Century, urban planning became a more prominent factor in how city officials developed strategies for future growth. Jane Jacobs, in her book The Death and Life of Great American Cities (1961) took aim at city planners who sought to manipulate or control the way their cities would develop without consideration of the benefits of "vertical" (i.e., high-rise apartment complexes) growth within urban areas. Jacobs firmly believed that, by encouraging "horizantal" growth -- in effect, the spread of communities to outlying or rural areas -- city planners, especially those who sought to apply the so-called "modernist" model involving intricate strategies for planned societies, were condemning their cities to a slow death. These strategies, she argued, ignored the contributions of the diversity that dominated in less-planned downtown areas in creating vibrant and culturally-rich neighborhoods.
Urban models rarely fully account for the evolutions that occur within cities and towns, especially in democratic countries where people are free to move around as they wish and buy and develop properties within the parameters of zoning regulations. And, long-term urban models frequently cannot account for radical economic and social changes that accompany industry growth and collapse and gentrification of lower-income urban communities.
Certain urban models have proven particularly successful and resilient, including the late 19th Century "Garden City Movement," which entailed the planned development of neighborhoods, often vertical, surrounding large community parks and wide main streets. The introduction in the early 20th Century of the modernist model, however, saw an emphasis on horizontal (i.e., urban sprawl) growth that resulted in dilapidated downtown areas and the growth of slums. Cities like Washington, D.C. (where this educator resided for 25 years) and Los Angeles (where he lived for five years before that) represent the culmination of the modernist approach, with large-scale urban sprawl pushing middle-class neighborhoods outwards and limited vertical housing in city centers. The result has been the requirement for large freeway systems (especially in Los Angeles) and the worst commuter traffic in the country.
Cities grow according to their ability to attract cutting-edge industries, to retain those industries, and to plan the infrastructure improvements necessary to accommodate the growth of those industries. Some cities have been economically dependent upon industries that for one reason or another die away. A classic example of this was cities like Pittsburgh and Cleveland that had been heavily dependent upon the steel industry. When that industry shrank due to foreign competition, those cities suffered. Pittsburgh was able to reinvent itself; Cleveland has been less successful. Similarly, the United States once had a vibrant shipbuilding industry that supported hundreds of thousands of jobs. When that industry perished during the 1980s, cities where the shipyards were located suffered.
Urban models can help, but they can't predict the future.