This chapter has examined how interactive computer graphics technologies can assist us in better under standing 3-D geospatial environments. The approaches range from those that are a simulation of the real world a virtual environment (VE) to those in which our view of the real world is combined with computer-based information (a mixed environment (ME)). An example of a geospatial VE would be your taking a tour through a simulation of how the 3-D landscape changed during major glaciations of North America. (Technically, we restrict the term VE to the situation in which you have some control over the tour, if you had no control, then the tour would be termed an animation.) An example of an ME would be you’re looking at the present-day landscape and seeing past glacial features overlaid on the landscape. Thus far, VEs are more common than MEs, but in the future, MEs might prove to be more useful, particularly for geographic fieldwork. We considered several technologies for creating VEs, including desktop, wall-sized, head-mounted, drafting table-format, and room-format displays. A distinct advantage of the latter three is that they allow the user to become more immersed in the VE-he or she might actually feel a sense of presence, of being in the VE even though it is artificial. Today, most VEs are experienced visually, although it is possible to utilize the full range of senses, including sound, touch, smell, taste, and body movement.