Geographical information systems are increasingly in demand by environmental resource and planning agencies, but the technical principles have been scattered throughout a wide range of disciplines, including cartography, spatial statistics, and computer science. The first study to gather together and explain these principles, this volume describes the major components of geographical information systems, including raster and vector data structures, modules for data input, digital terrain models, and methods of spatial analysis, classification, and interpolation. In addition, the book provides a much-needed critical review of the sources of error in geographical information processing.