La morphologie des tissus urbains et périurbains à travers une lecture fractale

L’étalement urbain génère des tissus bâtis dont la forme paraît souvent irrégulière, sans forme apparente. Ce phénomène atteint des zones de plus en plus éloignées des centres urbains ce qui est certes discutable sous l’aspect d’un développement durable. Cependant les solutions proposées pour maîtriser l’étalement urbain recourent souvent à des modèles classiques qui s’inspirent de la ville compacte et dense. Or il est connu que ces solutions sont souvent mal accueillies par la population concernée. Nous présentons dans cet article une autre approche de la forme de ces tissus urbains qui montre que leur organisation spatiale suit, en dépit de leur aspect irrégulier, une logique particulière qui peut être décrite par la géométrie fractale. Ceci permet d’appréhender d’une autre manière les raisons socio-économiques de ce phénomène et de développer une autre approche conceptuelle de la gestion de l’étalement urbain.Urban expansion produces an irregular urban fabric. This phenomenon influences areas which are distant from urban centres, a problem for sustainable development. Solutions proposed to reduce urban expansion are modelled on the pattern of the compact town. Generally, it is believed that these solutions are unacceptable to the people concerned. In this article we present an alternative approach to the study of urban fabric, which shows that, despite their irregular form, it is possible to describe their development using fractal analysis. This permits understanding of the socio-economic causes of this process and the development an alternative conceptual approach to the management of urban expansion.Zeichnet man die bebaute Fläche von Städten als « Schwarzplan » so entstehen Grundrissmuster, deren Form und randliche Abgrenzung auf den ersten Blick irregulär erscheinen. Dieses Phänomen steht in starken Widerspruch zum Paradigma der « verdichteten, kompakten Stadt », das von vielen Autoren als Paradigma nachhaltiger Stadtentwicklung betrachtet wird. Von der Stadtbevölkerung selbst werden aber solche verdichteten Strukturen weniger akzeptiert. Dort verdichten sich auch Vandalismus und andere Delikte. In diesem Artikel wird ein anderer Ansatz präsentiert, der nachweist, dass die scheinbar irregulären, offenen Grundrissmuster und Ränder von Städten einer Logik folgen, die als fraktale Geometrie beschrieben werden kann. Diese Geometrie ist nicht weniger « logisch » als die kompakte, sie hat aber anders als diese keine ideologischen Wurzeln, sondern folgt sozio-ökonomischen Bedingungen. Akzeptiert man diese Logik kommt man zu einer ganz anderen Bewertung der Stadtmuster

Mathematics and Morphogenesis of the City: A Geometrical Approach

Cities are living organisms. They are out of equilibrium, open systems that never stop developing and sometimes die. The local geography can be compared to a shell constraining its development. In brief, a city's current layout is a step in a running morphogenesis process. Thus cities display a huge diversity of shapes and none of traditional models from random graphs, complex networks theory or stochastic geometry takes into account geometrical, functional and dynamical aspects of a city in the same framework. We present here a global mathematical model dedicated to cities that permits describing, manipulating and explaining cities' overall shape and layout of their street systems. This street-based framework conciliates the topological and geometrical sides of the problem. From the static analysis of several French towns (topology of first and second order, anisotropy, streets scaling) we make the hypothesis that the development of a city follows a logic of division / extension of space. We propose a dynamical model that mimics this logic and which from simple general rules and a few parameters succeeds in generating a large diversity of cities and in reproducing the general features the static analysis has pointed out.Comment: 13 pages, 13 figure

Foreword

Web services advocate loosely coupled systems, although current loosely coupled applications are limited to stateless services. The reason for this limitation is the lack of a method supporting matchmaking of state dependent services exemplarily specified in BPEL. In particular, the sender’s requirement that the receiver must support all possible messages sent at a certain state are not captured by models currently used for service discovery. Annotated deterministic finite state automata provide this expressiveness. In this paper the transformation of a local process specification given in BPEL to annotated deterministic finite state automata is presented

Analyse des structures urbaines en France

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Clustering patterns of urban builtup areas with curves of fractal scaling behavior

Fractal dimension is an index which can be used to characterize urban areas. The use of the curve of scaling behaviour is less common. However, its shape gives local information about the morphology of the built-up area. This paper suggests a method based on a k-medoid for clustering these curves. It is applied to forty-nine wards of European cities, and shows that the curves add interesting intraward information to our knowledge of the spatial variation of the urban texture. Moreover, morphological similarities are observed between cities: living, architectural, and planning trends are not specific to individual cities

Simulating and assessing prospective scenariosA comparative approach in urban planning

The first part of the paper is centred on the phenomena of urban growth, in order to set the rules for a sustainable scenario of urban development. Then we enter the core of the paper that is the comparison of models. For each of the three compared models, we describe its main theoretical characteristics, the chosen parameters, and the obtained results. In section 6, heterogeneity of the produced results is discussed, and we highlight the points of interest and the lacks of the three models. Here we show that results we obtained feed debates about urban growth management. Finally, concluding remarks at the end of the paper address the general topic of the evaluation of the quality of simulation results.