Pa Longley

The emergence of geoportals and their role in spatial data infrastructures

Abstract Geoportals are World Wide Web gateways that organize content and services such as directories, search tools, community information, support resources, data and applications. This paper traces the emergence of geoportals, outlining the significance of developments in enterprise GIS and national spatial data infrastructures (SDIs), with particular reference to the US experience. Our objectives are principally pedagogic, in order to relate the development of geoportals to SDI initiatives and to review recent technological breakthroughs––specifically the development of direct access facilities for application services and metadata records, and the facility to utilize services directly from conventional desktop GIS applications. We also discuss the contributions that geoportals and SDI have made to simplifying access to GI, and their contribution to diffusing GI concepts, databases, techniques and models. Finally, the role of geoportals in electronic government (e-Government) is considered.

Urban Growth and Form: Scaling, Fractal Geometry, and Diffusion-Limited Aggregation:

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.

The fractal simulation of urban structure

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.

Geocomputation, Geodemographics and Resource Allocation for Local Policing

The field of geodemographics is one of the most fertile applications areas of geocomputation research. Geodemographic profiles of the characteristics of individuals and small areas are pivotal to tactical and strategic resource management in many areas of business, and are becoming similarly central to efficient and effective deployment of resources by public services. In this context, this paper describes research that has been developed in partnership with the Devon and Cornwall Constabulary and Institute of Criminal Justice Studies (ICJS) at the University of Portsmouth to assess the potential use of geodemographics as a policing tool. Crime, the fear of crime and the efficacy of public services are issues that have moved to the top of the UK political agenda and have long been matters of serious public concern. This paper considers the ways in which police forces might use geodemographics to better deploy resources at a variety of spatial scales in England and Wales.

On the Measurement and Generalisation of Urban Form

Developments in the provision and quality of digital data are opening up possibilities for more detailed measures of the form of urban areas. This paper begins with a review of some of the new data sources that are available in the United Kingdom, specifically the Ordnance Surveys ADDRESS-POINT product. The authors go on to develop a fine-scale data model of population densities, and fractal measures of the way in which urban development fills space. The research findings are compared with those of previous research that used less detailed data models.

Spatial Dependence and Heterogeneity in Patterns of Hardship: An Intra-Urban Analysis

Abstract Developments in the provision and quality of digital data are creating possibilities for spatial and temporal measurement of the properties of socioeconomic systems at finer levels of granularity. In this article, we suggest that the “lifestyles” datasets collected by private sector organizations in the U.K. and the U.S. provide one such prospect for better inferring the structure, composition, and heterogeneity of urban areas. Using a case study of Bristol, U.K., we compare the patterns of spatial dependence and spatial heterogeneity observed for a small-area (“lifestyles”) income measure with those of the census indicators that are commonly used as surrogates for it. This leads first to an exploration of spatial effects using geographically weighted regression (GWR) and then to a specification of spatial dependence using a spatially autoregressive model. This analysis extends our understanding of the determinants of hardship and poverty in urban areas; urban policy has hitherto used aggregate, outdated, or proxy measures of income in an insufficiently critical manner, and techniques for measuring spatial dependence and heterogeneity have usually been applied at the regional, rather than intra-urban, scales. The consequence is a limited understanding of the geography and dynamics of income variations within urban areas. The advantages and limitations of the data used here are explored in the light of the results of our statistical analysis, and we discuss our results as part of a research agenda for exploring dependence and heterogeneity in research focusing on the intra-urban geography of deprivation.

People of the British Isles: preliminary analysis of genotypes and surnames in a UK-control population

There is a great deal of interest in a fine-scale population structure in the UK, both as a signature of historical immigration events and because of the effect population structure may have on disease association studies. Although population structure appears to have a minor impact on the current generation of genome-wide association studies, it is likely to have a significant part in the next generation of studies designed to search for rare variants. A powerful way of detecting such structure is to control and document carefully the provenance of the samples involved. In this study, we describe the collection of a cohort of rural UK samples (The People of the British Isles), aimed at providing a well-characterised UK-control population that can be used as a resource by the research community, as well as providing a fine-scale genetic information on the British population. So far, some 4000 samples have been collected, the majority of which fit the criteria of coming from a rural area and having all four grandparents from approximately the same area. Analysis of the first 3865 samples that have been geocoded indicates that 75% have a mean distance between grandparental places of birth of 37.3 km, and that about 70% of grandparental places of birth can be classed as rural. Preliminary genotyping of 1057 samples demonstrates the value of these samples for investigating a fine-scale population structure within the UK, and shows how this can be enhanced by the use of surnames.

Morphology from imagery: detecting and measuring the density of urban land use

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.

Fractal-Based Description of Urban Form

Fractals, shapes with nonintegral or fractional dimension which manifest similar degrees of irregularity over successive scales, are used to produce a consistent measure of the length of irregular curves such as coastlines and urban boundaries. The fractal dimension of such curves is formally introduced, and two computer methods for approximating curve length at different scales—the structured walk and equipaced polygon methods—are outlined. Fractal dimensions can then be calculated by performing log-log regressions of curve length on various scales. These ideas are tested on the urban boundary of Cardiff, and this reveals that the fractal dimension lies between 1.23 and 1.29. The appropriateness of fractal geometry in describing man-made phenomena such as urban form is discussed in the light of these tests, but further research is obviously required into the robustness of the methods used, the relevance of self-similarity to urban development, and the variation in fractal dimension over time and space.

FRACTAL MEASUREMENT AND LINE GENERALIZATION

This paper describes a standard linear regression formulation through which the fractal dimension of cartographic lines may be ascertained. Four different algorithms for measuring the fractal character of lines are introduced: these are termed the structured walk, equipaced polygon, hybrid walk, and cell-count methods. The relative merits of these four methods are assessed using a digitized database which depicts the town of Cardiffs (U.K.) urban growth during the period 1886–1949. A concluding section assesses the methodological and substantive rationales for this measurement task.