La mesure de l'étalement urbain avec le plan cadastral informatisé, méthode et limites.

Depuis 2002, la Direction Générale des Impôts (DGI) a lancé un grand projet de numérisation du cadastre en France qui se traduit par la réalisation d'un plan cadastral informatisé (PCI). Celui-ci est actuellement disponible soit en format raster (PCI raster), soit en format vecteur (PCI vecteur). Même si le territoire n'est pas entièrement couvert, la vectorisation du cadastre a été effectuée en concertation avec la DGI sur la quasi-totalité des grandes villes françaises. Le PCI vecteur représente à ce titre une des seules bases de données foncières cartographiques à grande échelle. Comme toute information géographique, le PCI vecteur est structuré en deux parties : une partie graphique qui représente les parcelles et les bâtiments et une partie attributaire qui reprend les informations de la matrice cadastrale. Cette matrice contient entre autres, des informations temporelles sur les dates de construction des bâtiments. Dans un premier temps, cet article s'attache à décrire ces données et l'intérêt qu'elles représentent pour l'analyse rétrospective de l'évolution morphologique de la ville. Dans un second temps, l'article décrit une méthode d'utilisation de ces données à l'aide de deux outils. Il s'agit pour le premier du logiciel Google Earth qui permet de réaliser une visualisation dynamique de l'apparition de bâtiments en 3D sur un espace donné. Le second outil se présente sous la forme d'un module additionnel développé dans un système d'information géographique. Celui-ci propose, en plus d'une fonction de visualisation dynamique, une fonction d'analyse spatio-temporelle permettant de mesurer la vitesse d'apparition de différents objets. Ce module a été développé dans le cadre d'une étude sur l'étalement urbain mené en partenariat avec la Communauté d'Agglomération de La Rochelle. L'outil aide à analyser, à l'échelle du bâti et de la parcelle, l'évolution morphologique générale de la ville sur une période temporelle relativement longue : du milieu du vingtième siècle à nos jours. Outre une mesure de l'évolution horizontale dynamique de la ville (étalement), l'outil propose aussi une mesure " volumétrique " de cette évolution à partir du croisement des données cadastrales avec une base de donnée topographique à grande échelle fournie par l'Institut Géographique National (BDTOPO). Pour finir, cet article présente les avantages et les limites d'utilisation du plan cadastral informatisé vecteur en soulignant en particulier les manques et les erreurs qui ont été le plus fréquemment relevés durant cette étude. L'observation de ces artefacts permet d'envisager non pas une correction qui s'avérerait trop fastidieuse et dont la description dans cet article n'est pas l'objet, mais une estimation de leur impact sur la qualité générale des mesures obtenues

Insights on cadastral information uses for a diachronic space & time analysis: The case of urban spread in La Rochelle (France)

La Rochelle, France knew during the second half of the twentieth century an important increase of its permanent and seasonal population. Since 1999, the city is grouped together with 17 others municipalities (communes) into an intercommunality (cooperation group between communes) : La Rochelle's community of Agglomeration (CDA-LR) (fig 1). Because of an attractive coastal position, the CDA-LR is subjected to a strong growing of population. It showed itself by a massive urban spread. This urban spread is constrained by a coastal position (physical constraints and planning regulations). This urban spread is today particularly visible in the peripheral municipalities (Communes) of the CDA-LR. These municipalities absorb the inhabitants because they cannot find a housing in the city of La Rochelle. The CDA-LR is under a strong land pressure because of its attractive coastal position. The land is very regulated and the built is already very dense. Inhabitants are thrown back towards the peripheral by the price of the housing. The mastery of the urban spreading of the CDA-LR is one of stakes of the future land development plan (schema de coherence territorial : SCOT). The SCOT is at present in progress. The aim of this paper is to propose space and time analysis tools in order to study the urban spread phenomenon. These tools are implemented in a geographical information system. Cadastral dataset is used as an input

Vers une simulation de l'évolution des structures urbaines à partir d'agents

Ce document présente un modèle d'évolution urbaine à base d'agent

Evaluation of urban planning strategies with a versatile urban growth model

International audienceLa Rochelle, France witnessed an important growth of its permanent and seasonal population during the second half of the twentieth century. Its attractive coastal position is the main reason for this increase, which led to a massive urban spread, particularly in La Rochelle peripheral municipalities. Which are the strategies used by local public authorities to take into account social and environmental problems? While it has been very innovative since 1970 in regard to urban ecology and sustainable development, does La Rochelle still have today the capacity to tend towards the \“ideal sustainable city”? On the contrary, is La Rochelle powerless, or even more complicit in the urban sprawl phenomenon? The purpose of this paper is to focus on one factor that particularly influences urban growth: local urban policies and planning strategies through planning documents analysis. For this, an urban growth model based on a cellular automata paradigm is used. In this model, the space is described as a grid, for each non built cell, with a graduated probability of building. This probability of building is based on the analysis of planning rules (e.g. urban planning regulation framework). The example of the correlation between these planning rules and local urban growth is described in this paper. The model enables the simulation of alternative urban growth scenarios. It helps one to estimate how alternative planning could affect non built areas. This model aims at helping the elaboration of future planning documents. The control of La Rochelle’s urban spread is one of the main stakes to be taken into account in the future land development plan (Schema de COherence Territoriale: SCOT). The SCOT is currently being elaborated in La Rochelle

Impact of relief accuracy on flood simulations and road network vulnerability analysis

The increased availability and accuracy of multi-sources data enhance the simulation quality of natural disasters (hazard). Moreover, it enables a better prediction of their impact on the territory (vulnerability). Numerical representation of relief (DTM) is a prime necessity in risk simulation, in particular in flood study. Integrating 2D objects into a DTM significantly improves the relief representation around each object. The aim of this paper is first to enrich the relief accuracy with the altimetric attributes of 2D vector objects, and then to assess the impact of these modifications within the context of a rise in the water level and its consequences on the road network vulnerability. The first part focuses on the integration of 2D vector data (e.g. roads) on a 2.5D digital terrain model. The integration of 2D vector data on a DTM usually raises data consistance issues. These data often stem from different acquisition modes ; moreover, their scale and their dimension (2D, 2.5D, 3D) vary according to their nature and the data capture. In order to overcome these problems, our approach consists in converting 2D vector data in 2.5D vector data by assigning them a width and computing their elevation. Then, these latter are integrated into the DTM and make it sharper, especially on the former interpolated areas. In a second part, we analyze the floods effects on the running of the road network in Orléans (France). In addition to the direct damages caused by the physical action of the water, the flood also leads to functional disruptions on the road network by forcing users to take detours. In a risk preventive viewpoint, the network administrator has first to consider a given flood scenario and consequently to identify the network components to be protected as a priority, in order to reduce to the minimum the costs induced by the detours. On account of both levels of precision considered in the original DTM and in the enriched DTM, we have to compare two damaging scenarios of the road network for a given flood hazard. To that end, we quantify the functionality of the network components with centrality measures and we compare the efficiency of the different configurations of damaged network with accessibility measures. The results of this study prove how much the flood of the road network, the induced functional disruptions and the associated preventive actions depend on the adopted precision in the representation of the terrain

A multi scale morphological interpretation of the sustainable city

International audienceThis article seeks to highlight a shift in development of the city towards a sustainable model through the prism of morphology. It presents multi-scale, morphological keys for understanding, making it possible to identify and detail the physical and structural elements which comprise the sustainable city. Via these keys for understanding, the article endeavours to identify the various physical elements and structures of this urban landscape which is undergoing radical transformation. On what scale is the drive towards a sustainable city the most noteworthy? Does the slogan \“act locally, think globally” also apply to the urban territory? This paper begins by outlining the concepts of the sustainable city. There then follows a description and analysis of morphological keys for understanding the sustainable city. Finally, the concluding part covers application of these keys to the city of Nantes, which hosts several sustainable development projects and will assume the mantle of European Green Capital in 2013

Analysis of ecological inequalities in residential strategies to improve sustainability of urban coastal area

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Synthesis and evaluation of a tri-tyrosine decorated dextran MR contrast agent for vulnerable plaque detection

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