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Cartographie semi-automatisée et multi-sources de la couverture du sol. 1. Périmètre de l'agglomération franco-valdo genevoise (CCSA04, moyenne résolution)

Published inArchives des sciences, vol. 62, p. 107-124
Publication date2009
Abstract

Semi-automated, multi-source cartography of land cover. 1. Geneva transboundary area (medium resolution). - A land cover map is an essential layer of information for the management and planning of the territory. Within the context of a trans-boundary endeavour between Switzerland and France (Projet d'Agglomération Franco-Valdo-Genevoise, here- after AFVG), a medium-resolution land cover map (CCSA04) was developed for the Canton of Geneva, part of the Canton of Vaud, and parts of the French departments of Ain and Haute-Savoie. Within the constraints of the available data, a 27-class legend was chosen to suit the needs of the AFVG project. This leg- end can be converted to the Swiss OTEMO and European CORINE standards. The applied mapping methodology can be described as multi-source, multi-scale and object-oriented. Multi-source refers to using the SPOT satellite imagery at two dif- ferent resolutions (5m for the visible bands, 10m for the infrared), a Digital Elevation/Digital Height Model, and several vec- tor layers. Multi-scale means that the analysis, within the Definiens DeveloperTM software, proceeded on different levels or scales. The object-oriented approach is based on the concept that the semantic information necessary to interpret an image is not contained in isolated pixels, but rather in objects and their mutual relationships. These objects, obtained through a segmentation process, were classified using multiple criteria, such as their spectral values, morphology and context. Some legend classes, such as buildings and roads, are defined by their spatial coincidence with a shapefile. Others, such as forests and water, are derived from their spectral values. The altitude criterion was used to differentiate mountain grasslands from low-altitude meadows . The automated classification process was completed by some manual editing in the following cases: objects adjacent to roads, under-estimation of coniferous forest, agricultural surfaces falsely classified as deciduous forest, confusion between hard surfaces and bare soil, and objects hidden by shadows. In order to control the quality of the land cover map, a statistical procedure was applied. Two control points were randomly selected within each square kilometre of the AFVG area, and their land cover class was visually estimated from colour aerial photographs, based on a simplified legend. A contingency matrix was computed, yielding a Kappa coefficient of 89%, which exceeds the mandatory threshold of 75% requested by the project. It is considered that this quality level is quite acceptable, owing to the difficulties stemming from the heterogeneity of data between the Swiss and French entities: vector layers having different meaning and showing mismatch across the border, and the SPOT mosaic being a composite of scenes from two years, resulting in differences in radiometry. The rugged topogra- phy in the Jura and pre-Alps also leads to extensive zones of shadows, which complicate the analysis. As an example of application of the CCSA04 map, land cover statistics were computed for the four entities. Finally, recom- mendations are presented towards an improvement of the map-making process (revised legend, compatible data across bor- ders and better imagery), in the perspective of future applications such as change mapping for the computation of land cover trends.

Keywords
  • Land cover mapping
  • Object-oriented approach
  • Medium resolution remote sensing
  • Switzerland
  • France
Citation (ISO format)
SCHWARZER, Stefan, ALLENBACH, Karin, JAQUET, Jean-Michel. Cartographie semi-automatisée et multi-sources de la couverture du sol. 1. Périmètre de l’agglomération franco-valdo genevoise (CCSA04, moyenne résolution). In: Archives des sciences, 2009, vol. 62, p. 107–124.
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  • PID : unige:32677
ISSN of the journal1661-464X
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