Raster-Mode Area Generalization for Land Use and Land Cover Maps

Raster mode is more appropriate than vector mode for the computer-assisted generalization of land use and land cover data. A raster-mode approach promotes the partitioning of thin or insignificant polygons and the growing or linking of others. If the scale is reduced substantially, partitioning and region growing are needed to guarantee a graphically stable image, which will resist misregistration during reproduction. The test examples presented here demonstrate the efficacy of a raster-mode approach in reducing 1 : 250,000-scale land use and land cover data in the U.S. Geological Survey's Geographic Information Retrieval and Analysis System (GIRAS) to 1 :2,000,000, the scale of the National Atlas series of regional reference maps. A variety of category weights and priority rankings and several nonmutually exclusive options for smoothing and data aggregation confront the map author, who must provide detailed specifications. With these techniques generalized land use and land cover maps can be biased to emphasize a category or a combination of categories.