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American society is a very mobile one, with approximately twenty percent of the populace changing its place of residence every year. It has been estimated that over two-thirds of all moves take place within the city. Geographic studies of intra-urban migration generally treat the relocations as either 1) movement from one areal unit to another, such as inter-census tract flows, or as 2) individual-level, unrelated moves between respective origins and destinations. In reality, however, each change of residence is one part of a much longer sequence of changes.
This thesis examines intra-city moves within the framework of their real-world linkage by utilizing the concept of the vacancy chain. The work emphasizes the spatial manifestations and geometric character of intra-urban residential movement by using the vacancy chain to describe, analyze, and explain the patterns. More specifically, the research attempts to statistically identify intra-city "channels of migration," whose existence has been postulated by several scholars (though none has substantiated the notion). The study is based upon 1972 mobility data collected by three utility companies for Lincoln, Nebraska.
Principal findings of a geographic nature include the fact that 65.9% of the intra-urban changes of residence were 2.99 miles or less in length. In general, the length of a link was found to be inversely related to its position in the chain with the first "link" (the initial move to the urban periphery) being the longest. Similarly, there tended to be an inverse relationship between directional bias and link number with the angles of moves in central parts of the city being more "random" than those for the outer areas. The vacancies in the sequences of moves tended to "move" closer to the Central Business District and the level of “clustering” of the move-origins decreased as one moved further back in those sequences. The four statistics developed to quantify the geometric alignment of each vacancy chain allowed only 20.3% of the chains to be correctly grouped according to the neighborhood of origin. Therefore, the multivariate classification failed to substantiate the existence of "migratory streams" within the city.
The "housing-environment" analysis determined that 71.1% of the vacancy chains ended in census tracts that were below the mean dollar-value of the city's owner-occupied homes, with 58.5% terminating in tracts that were one standard deviation below the mean and 12.6% in tracts that were two standard deviations below average. The sequences, however, generally did not continue to the poorest areas of the city. In all, 72.7% of the movers migrated to a "better" housing environment, but the extent of the "upward-filtering" decreased as link number increased. "Reverse-filtering," then, tended to become more prevalent as chains lengthened. A statistically significant difference was found between the "upward-" and "downward-filterers" as the average level of increase for the former group was $10,105 while the decrease for the latter group was only $ 5,059. The multivariate analysis of the "filtering indicators" allowed correct classification of 42.2% of the vacancy chains but much of the discriminatory power rested merely on the home values in the neighborhoods where the sequences originated.
The principal hypothesis of the dissertation, dealing with the statistical identification of intra-city "migratory streams," had to be rejected because the four developed spatial indices did not allow consistent and accurate grouping of vacancy chains. Despite this fact, the author believes that "vacancy-chain analysis" has great potential, especially for research involving large metropolitan areas.
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