Suchergebnisse

This paper is addressed to the problem of developing realistic-looking patterns of land use and activity from predictions generated by conventional urban models. The method developed is based on a geometric model of irregularity involving hierarchical cascading and recursion, whose rationale lies in the emergent field of fractal geometry. First the idea of fractals—shapes with fractional dimension—is introduced and then it is shown how two-dimensional patterns whose dimensions are consistent with a large city such as London can be simulated at different levels of detail or recursion. It is then argued that the hierarchical structure of cities should be exploited as a basis for such simulation, and it is argued that discrete choice models of individual spatial behaviour have excellent properties which enable their embedding into such simulations. The standard multinomial logit model is presented and then applied to house-type data in Greater London. A variety of models are estimated, house-type choice being related to age and distance from the centre of the city, and the spatial biases in these predictions are then mapped using prediction success statistics. These models are then used at the base level of a fractal simulation of house type and location in London. Random and deterministic model simulations are developed, and an unusual and possibly innovative feature of these simulations involves the way the inputs and outputs, data and predictions, are simultaneously displayed on the graphics device used. Conclusions for further research, particularly in spatial hierarchical modelling, are then sketched.

In this paper the detailed patterns of British property valuation and local revenue raising under the council tax are compared with those prevailing under the domestic rates. The results of matching individual council-tax valuations with rateable values for the 47000 domestic properties that make up the Inner Area of Cardiff, Wales, are reported. A geographical information system is used to identify the disaggregate pattern of properties which have been assigned higher or lower relative values after the abolition of the domestic rates. The findings are seen as significant in describing the intraurban geography of property values in Britain: properties constructed by local authorities now attract significantly lower relative valuations; pre-1919 private-sector housing is now more highly valued; and different construction types (for example, purpose-built flats, converted flats, and ends of terraces) attract quite different valuations under the two regimes. Overall, the distribution of rateable values vis-à-vis that of council-tax bands is likely to have had a multifaceted effect upon local revenue raising, and the authors begin to explore its changed geography in some detail.

The United Kingdom has experienced different local taxation regimes in each of the last three financial years: Namely the property-based household rates; the personal community charge or 'poll tax'; and the hybridised personal community charge adjusted for neighbourhood 'transitional relief'. The geographical impact of these changing policies in the Inner Areas of the City of Cardiff is examined, highlighting the importance of historical rateable values and household sizes. By using a purpose-built street-level database, the implications of the different taxation systems are examined at increasingly detailed geographic scales, and the complexity of their impact is illustrated. This analysis focuses upon the geographical effects of using administrative community boundaries for the allocation of transitional relief in Cardiff, Wales.

In this paper, we propose a model of growth and form in which the processes of growth are intimately linked to the resulting geometry of the system. The model, first developed by Witten and Sander and referred to as the diffusion-limited aggregation or DLA model, generates highly ramified tree-like clusters of particles, or populations, with evident self-similarity about a fixed point. The extent to which such clusters fill space is measured by their fractal dimension which is estimated from scaling relationships linking population and density to distances within the cluster. We suggest that this model provides a suitable baseline for the development of models of urban structure and density which manifest similar scaling properties. A typical DLA simulation is presented and a variety of measures of its structure and dynamics are developed. These same measures are then applied to the urban growth and form of Taunton, a small market town in South West England, and important similarities and differences with the DLA simulation are discussed. We suggest there is much potential in extending analogies between DLA and urban form, and we also suggest future research directions involving variants of DLA and better measures of urban density.

Defining urban morphology in terms of the shape and density of urban land use has hitherto depended upon the informed yet subjective recognition of patterns consistent with spatial theory. In this paper we exploit the potential of urban image analysis from remotely sensed data to detect, then measure, various elements of urban form and its land use, thus providing a basis for consistent definition and thence comparison. First, we introduce methods for classifying urban areas and individual land uses from remotely sensed images by using conventional maximum likelihood discriminators which utilize the spectral densities associated with different elements of the image. As a benchmark to our classifications, we use smoothed UK Population Census data. From the analysis we then extract various definitions of the urban area and its distinct land uses which we represent in terms of binary surfaces arrayed on fine grids with resolutions of approximately 20 m and 30 m. These images form surfaces which reveal both the shape of land use and its density in terms of the amount of urban space filled, and these provide the data for subsequent density analysis. This analysis is based upon fractal theory in which densities of occupancy at different distances from fixed points are modeled by means of power functions. We illustrate this for land use in Bristol, England, extracted from Landsat TM-5 and SPOT HRV images and dimensioned from population census data for 1981 and 1991. We provide for the first time, not only fractal measurements of the density of different land uses but measures of the temporal change in these densities.