Michael F. Goodchild is Professor of Geography at the University of California, Santa Barbara, and Director, National Center for Geographic Information and Analysis. He was Editor of Geographical Analysis between 1987 and 1990 and has served as Chair of the GIS Specialty Group of the Association of American Geographers. Dr. Bradley O. Parks is GIS Coordinator for Great Lakes Research at the U.S. Environmental Protection Agency's Large Lakes Research Station, Grosse Ile, MI. Dr. Louuis T. Steyaert is a research physical scientist within the National Mapping Division of the U.S. Geological