Visualizing large amounts of information interactively is one of the most attractive and useful capabilities of GIS. High-powered computers can alter any element of the display "on the fly," changing not only the look of the graphic image but also its interpretation. This ability to create multiple perspectives -- both literally and figuratively -- enhances a viewer's perceptive abilities to understand the phenomenon being studied like never before.
Visualizing data using current computing technology and interactive GIS has many advantages over doing so using traditional paper maps. The following is a partial list, one that grows with each new version of software and each new advance in hardware.
• GIS is fully interactive. Adding new fields of data, taking them off, changing the color scheme or form of the map, adding text, moving symbols, and a host of other capabilities give a user tremendous flexibility and power.
• GIS displays are zoomable and pannable. Moving around in the display offers a user new perspectives, greater (or less) detail, and new insight.
• Users can take advantage of computationally intensive functions such as "draping" a perspective view over a surface (like a digital elevation model) or creating the impression of three dimensions on a 2D display (the computer screen) using complex rendering and shading algorithms.
Many of the tips and guidelines outlined in this unit were developed by cartographers over many decades for the design of paper maps. They are all relevant to the design of interactive displays within GIS. In fact, with the vast array of choices facing a GIS display designer and with the luxury of complete interactivity, awareness of the power of the visual image to persuade a viewer has never been more important.