Geographic Information Systems: An Introduction, 3rd Edition

7.3 Displays

The display (monitor) of a computer is the user's primary visual communication medium in all computer work. A display consists of a screen and its associated electronic circuitry. The screen itself is either the face of a cathode ray tube (CRT), similar to those long used in television sets and radar, or one of the newer, flat arrays of semiconductor elements, such as the liquid crystal displays (LCDs) used in laptop and notebook PCs. LCD technology is advancing, but at present the CRT remains the mainstay for almost all GIS applications because it produces more light, has higher resolution, and has a greater range of possible display colors than do LCDs. All CRTs are vacuum tubes and operate on the principle that a beam (ray) of electrons emitted by a cathode is focused and directed at an electroluminescent screen. The information displayed is refreshed periodically. Regeneration screen images are refreshed up to 60 times a second. As with TV images, the displays are based on rasters, and GIS vector map data are converted to raster data for screen presentation (Figure 7.8).

Color screens employ the three basic colors—red, green, and blue (RGB)—in varying intensities, which reproduce a wide range of hues. A high-resolution 19-inch (diagonal) screen designed for computer graphics may resolve 1600 points horizontally and 1280 points vertically. Screens are now available with processing functions that include vector–raster conversion, storage of vector data, and color ...