A pilot study to test the ability to map land cover of the metropolitan project Franco- Vaud-Geneva has been conducted by GRID-Europe for the Territorial Department of the Geneva Canton. The test was conducted on a sub-area of 120 km2, between Versoix and Divonne-les-Bains, representing 3% of total area.
Using raster data (SPOT mosaic 5-10 m resolution and MNA) and vector data from three political entities, a methodology for the extraction of thematic information has been tested and applied. This object-oriented process includes a multi-resolution segmentation of the image, producing vector objects (polygons), which are then labeled thematically based on multiple criteria (spectral, morphological, contextual). This methodology led to the CCSol Agglo-Pilot map, which reflects land cover using a legend with 23 classes. This map has an overall accuracy of 72% (as measured by the kappa coefficient). While the performance exceeds 80% for most classes, the borders of some buildings and urban green areas show classification errors reaching 70%. These difficulties are primarily due to the 10 m resolution of SPOT mosaic, which is of the same magnitude as urban objects.
The comparison between the high-resolution map available for the city of Versoix (CCSSol) and CCSol Agglo-Pilot in terms of statistical coverage of the soil showed little difference.
Some of the classification errors could be solved by improving basic data (removal of topographical changes, adding vectors for lakes and rivers) and the improvement of the algorithms implemented in the software eCognition used to analyse the images.
This pilot project was based on previous studies made by GRID-Europe from 2002. With the results obtained and by implementing the improvements suggested, it would be possible to produce a land cover map for the entire Geneva metropolitan area. The mandate for this new project was given to GRID-Europe and will be concluded in early 2009.