Yichun Xie

Modeling urban dynamics through GIS-based cellular automata

In urban systems modeling, there are many elaborate dynamic models based on intricate decision processes whose simulation must be based on customized software if their space–time properties are to be explored effectively. In this paper we present a class of urban models whose dynamics are based on theories of development associated with cellular automata (CA), whose data is fine-grained, and whose simulation requires software which can handle an enormous array of spatial and temporal model outputs. We first introduce the generic problem of modeling within GIS, noting relevant CA models before outlining a generalized model based on Xies (1996, A general model for cellular urban dynamics. Geographical Analysis, 28, 350–373) “dynamic urban evolutionary modeling” (DUEM) approach. We present ways in which land uses are structured through their life cycles, and ways in which existing urban activities spawn locations for new activities. We define various decision rules that embed distance and direction, density thresholds, and transition or mutation probabilities into the models dynamics, and we then outline the software designed to generate effective urban simulations consistent with GIS data inputs, outputs and related functionality. Finally, we present a range of hypothetical urban simulations that illustrate the diversity of model types that can be handled within the framework as a prelude to more realistic applications which will be reported in later papers.

From cells to cities

Since mathematical models came to be applied to problems of architectural and urban form, new concepts based on predicting large-scale structure from local rules have emerged through insights originating in computation and biology. The clearest of these are computer models based on cellular automata (CA) and their recent generalization in evolutionary biology and artificial life. Here we show how such models can be used to simulate urban growth and form, thus linking our exposition to the longer tradition of ideas in studies of built form emanating from the ‘Cambridge School’. We first review developments of CA in general and then in urban systems in particular. We propose a general class of CA models for urban simulation and illustrate two simple applications, the first a simulation of the development of the historical ‘cell’ city of Savannah, Georgia, the second, a generic hypothetical application. We then show how this generic model can be used to simulate the growth dynamics of a suburban area of a mid-sized North American city, thus illustrating how this approach provides insights into the way microprocesses lead to aggregate development patterns.

Possible urban automata

New developments in computation based on cellular automata (CA), which are finding widespread application in simulating evolution, are beginning to suggest that science is not simply about the study of actual phenomena but about potential or possible phenomena. This notion is central to design but the prospect of a new science through computation which enables systematic and formal study of ‘possible worlds’ has clear relevance to the scientific understanding of human systems such as cities. In this paper, we provide a framework for such understanding based on a generic model of the dynamics of urban systems. After formally presenting the framework, we show how it can be used to generate existing model structures which can be seen as samples from a wide, indeed infinite, array of possible forms. In fact, the emphasis here is not just upon possible model structures per se but upon possible urban forms which such structures are able to generate. Accordingly we formulate models in terms of ideas from CA which treat space and time in its most disaggregate or local form. We begin by developing models both of areal and of linear growth processes and then combine these into a more general structure which forms the basis for a comprehensive model of urban structure. We illustrate the varieties of form which such models can generate, concluding by suggesting that such an approach might constitute the basis for more systematic exploration of the space within which possible urban morphologies exist.

Preliminary Evidence for a Theory of the Fractal City

In this paper, we argue that the geometry of urban residential development is fractal. Both the degree to which space is filled and the rate at which it is filled follow scaling laws which imply invariance of function, and self-similarity of urban form across scale. These characteristics are captured in population density functions based on inverse power laws whose parameters are fractal dimensions. First we outline the relevant elements of the theory in terms of scaling relations and then we introduce two methods for estimating fractal dimension based on varying the size of cities and the scale at which their form is detected. Exact and statistical estimation techniques are applied to each method respectively generating dimensions which measure the extent and the rate of space filling. These methods are then applied to residential development patterns in six industrial cities in the northeastern United States, with an innovative data source from the TIGER/Line files. The results support the theory of the fractal city outlined in books by Batty and Longley and Frankhauser, but with the clear conclusion that different scale and estimation techniques generate different types of fractal dimension.

Modelling inside GIS : Part 1, Model structures, exploratory spatial data analysis and aggregation

Abstract This is the first of two papers elaborating a framework for embedding urban models within GIS. This framework is based upon using the display capabilities of GIS as the user interface to the conventional modelling process, beginning with data selection and analysis, moving to model specification and calibration, and thence to prediction. In this paper, we outline how various stages in this process based on purpose-built software outside the system, are accessed and operated through the GIS. We first deal with display based on thematic maps, surfaces, graphs and linked windows, standard to any data from whatever source, be it observations, model estimates or predictions. We then describe how various datasets are selected, how the spatial system can be partitioned or aggregated, and how rudimentary exploratory spatial data analysis enables scatterplots to be associated with thematic maps. We illustrate all these functions and operations using the proprietary GIS ARC-INFO applied to population data ...

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.

Modelling Inside GIS: part 2: Selecting and Calibrating Urban Models Using ARC-INFO

Abstract This is the second of two papers which elaborates a framework for embedding urban models within GIS. In the first paper (Batty and Xie 1994), we outlined how the display functions of a proprietary GIS could be used to organize a series of external software modules which contained the central elements of the modelling process, namely dataset selection and analysis, and model specification, calibration, and prediction. In that paper, we dwelt on display and data analysis functions whereas here we outline the model-based functions of the system. We begin by reviewing residential location models based on population density theory, stating continuous and discrete model forms, and calibration methods. We then illustrate a pass through the software using data for the Buffalo urban region, showing how observed data and model estimates can be evaluated through graphic display. We present ways in which the system can be used to explore and fit a variety of models to different zoning systems and in so doing...

Detecting spatiotemporal dynamic landscape patterns using remote sensing and the lacunarity index: a case study of Haikou City, China

Quantifying the landscape pattern and its dynamics is essential for the monitoring and assessment of the ecological consequences of urbanization. As one of the Special Economic Zones, Haikou is one of the fastest growing regions among all Chinese cities, owing to rapid real estate development. Using a GIS-based land-use dataset from 1986, 1996, and 2000, in combination with a lacunarity index, we attempt to quantify the spatial pattern in the Haikou metropolitan area. After the landscape structure changes over the periods 1986–96 and 1996–2000 are analyzed, a Markov conversion matrix is applied in order to study the sources and destinations of landscape dynamic changes. The lacunarity index is calculated in order to measure the landscape dynamics, with respect to several major land-use types, at a range of spatial scales. The findings indicate that the leapfrog development of real estate and the rapid economic growth of Haikou City have had a great impact on the dynamic landscape patterns. From 1986 to 1996 urban land expanded dramatically and clustered, while cropland was encroached upon and fragmented. From 1996 to 2000, after the government had implemented the strict cropland protection measures, urban expansion and cropland misuse were controlled to a large degree, and a lot of cropland was reclaimed in certain areas. We investigate the dynamic landscape pattern and process, and their implications in policy and economic development.

Site Planning and Guiding Principles of Hi-Tech Parks in China: Shenzhen as a Case Study

Recent institutional changes, marketization, and globalization have combined to bring about rapid economic growth in contemporary China. One of the direct outcomes is the rapid expansion of large cities and the recurring birth of new cities from small towns and rural villages. Clustered construction cranes are popular scenes in many Chinese cities. One of the noticeable city landmarks is the specialized economic development district, such as a hi-tech park, industrial park, commerce park, high-standard apartment complex, and designated port district. Along with the development of these new types of urban blocks, the Chinese policies and practices of urban planning and city design have been dramatically reshaped. This paper, on the basis of our participatory observation of the planning process of the Shenzhen Silicon Peak Software Ecological Park, examines site planning and design of hi-tech parks in China. The paper discusses the seven principles guiding the development of hi-tech parks, and the four implementation strategies directing planning and design practices. It also illustrates the adoption of GIS techniques, the new eco-community planning approach, and the classic Chinese cosmology—harmonious wind and water (feng shui)—through the case study. The paper concludes with discussion of the changes of Chinese values and practices of urban planning in the context of hi-tech parks in the transitional period.