Suchergebnisse

Some problems that must be resolved by the analyst in connection with the treatment of flows across system boundaries to and from external zones are discussed in this paper. These problems make it necessary to make modifications to the conventional formulations both of the doubly and of the singly constrained members of the family of spatial-interaction models. None of the possible modifications wholly satisfies theoretical requirements in terms of the doubly constrained model, and the advantages and limitations of various approaches can only be assessed in an operational situation. For this reason some of the findings from a study of the Amersfoort region are presented which help to throw light on this problem.

Some simple criteria for comparing the spatial systems that are used in different applications of doubly constrained interaction models are described and their usefulness is demonstrated by a comparative analysis of four models drawn from British, Dutch, and German sources. The influence that spatial representation has on the performance of the models is also examined and considerable differences are found between the four case studies. These effect the separate interpretability of the endogenously predicted variables and the rate at which the convergence criteria are satisfied.

In this case study of population forecasting and planning practice in South Yorkshire, a number of insights are given into the issues involved in the application of quantitative methods to policy analysis. It is suggested that the users of population forecasts typically question the validity of the data and the assumptions made about future trends rather than the form of the forecasting model itself. In the case study it is also demonstrated to what extent analysts have to account for the judgements they have made about these matters when the accuracy of their forecasts is challenged by parties with strong vested interests in the outcomes. In this way the constraints that are placed on analysts working within the planning process are highlighted, and attention is drawn to some of the advantages and disadvantages of their position.

Three alternative approaches (the functional distance approach, the iterative proportional fitting based procedure and the intramax procedure) to the functional regionalisation of spatial interaction data are compared and evaluated in this paper. After a general discussion of the basic properties of each approach, the detailed processes that are involved in each case are illustrated by reference to a worked example. The last section of the paper presents the findings obtained by each of these approaches as a result of empirical studies of Greater London, Merseyside, and the Netherlands. The study as a whole identifies a number of ambiguities in the existing literature which point to the need for a more rigorous examination of current methodology. They also suggest that more attention needs to be given to the role that is played by aggregation procedures as against data transformation procedures in the evaluation process. Although each user must decide which of the three methods best suits his particular purposes, the results obtained by means of the intramax procedure seem generally more readily interpretable than those obtained by either of the other two methods.