Digital spatial data are information pertaining to real-life features located on the surface of the Earth (Longley, Goodchild, Maguire, & Rhind, 1999). Such information is crucial to help us understand practical real-world issues, whether they are biological, environmental, or social, and whether they are historical or in real time (Fisher, Wenzhong, Goodchild, & Shi, 2002). Digital spatial data for general-purpose mapping (e.g., layers typically found in topographic maps, and other high-demand base layers useful for a wide variety of more specific thematic