Morphology from Imagery: Detecting and Measuring the Density of Urban Land Use

Abstract

Abstract. 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.

On the Measurement and Generalisation of Urban Form

“…In some of our previous work we have focused upon settlements which are not strongly constrained by their physical setting (for example, Longley and Mesev, 1997a). Here, however, our priority is to compare the new digital data infrastructure with what was previously available (Longley and Mesev, 1997a;Mesev et al, 1995) and thus our focus here will be upon Bristol. This is not ideal, as far as any quest for establishing space-filling`norms' is concerned, because Bristol's physical setting is characterised by varied topography and the physical constraint of the Avon Gorge, which abruptly truncates development to the west of the city.…”

“…In this paper, we will use the empirical study of Mesev et al (1995) as a baseline against which new morphological measures for the City of Bristol may be compared. Almost every record in ADDRESS-POINT is known by the Post Office to be in current use, although the file also contains other minor categories, such as properties under construction and other delivery points not in current use.…”

“…We will return to this point again in our discussion, when we will anticipate that ADDRESS-POINT forces us to clarify our thinking about what we actually mean by terms such as`density' and`space filling'. Mesev et al (1995) sought to detect and model the urban form of Bristol, by using data that were available in the mid-1990s. In their paper, they reported the successful creation of a hybridised socioeconomic and physical representation of Bristol, by using remotely sensed (RS) LANDSAT 5 Thematic Mapper (TM) satellite imagery and a population-surface transformation (Bracken and Martin, 1989) of small area 1991 Census data.…”

“…Using algorithms developed by Martin and Bracken (1991), Mesev et al (1995) used population-surface transformations of small area (enumeration district, ED) census data that were based upon distance decay from subjectively positioned digital population centroids to develop continuous population-density measures. These allow the data model to move beyond the uniform within-area density assumption implicit in choropleth representations and to reduce dependence on the geographical tessellation of census zones.…”

“…Our understanding of the morphology of urban land use is one area in which this is clearly the case, and previous research has begun to devise a number of measures of urban structure and space filling (Batty and Longley, 1988;Frankhauser, 1994). We have both contributed to a paper previously published in this journal (Mesev et al, 1995) which began to develop a hybrid data model using satellite measurements and the UK Census of Population. This paper also applied a number of morphological measures to the analysis of form, an approach which was developed using small area TIGER file data from the US Census by Batty and Xie (1996).…”