His research focuses on the modeling of environmental systems and makes extensive use of GIS software tools, fieldwork, spatial analysis techniques, and computer models. He has published numerous books and articles on these topics, including two edited volumes, Terrain Analysis: Principles and Applications (John Wiley and Sons, 2000) and the Handbook of Geographic Information Science (Blackwell Publishers, 2007), and Environmental Applications of Digital Terrain Modeling (John Wiley and Sons, 2018). Much of this work is collaborative and cross-disciplinary with the goal of improving knowledge and understanding of the factors linking society, the environment and human health. Among his numerous honors for his research and teaching are receipt of the University Consortium of Geographic Information Science (UCGIS) Lifetime Achievement in GIScience Education Award in 2019, his election as a Fellow of the UCGIS in 2014, receipt of a Lifetime Achievement Award by the International Association of Chinese Professionals in Geographic Information Science in 2016, the Mellon Award for Excellence in Mentoring from the Center for Excellence in Teaching at USC (2005) and the Albert S. Raubenheimer Outstanding Faculty Award for his research, teaching, and service contributions in Dornsife College at USC (2004).