Abstract: In a mapping system using a graphics application programming interface, for every digital terrain elevation data post, a normal to the terrain surface is calculated, which is then encoded in a half-polar coordinate system. The tilt and azimuth are represented as two fixed-point integers and a color table containing the illumination colors, such as gray scale colors, are given a particular azimuth and tilt combination. The two-dimensional color table array is collapsed into a single-dimensional array by concatenating (linking together) the azimuth and tilt into a single integer. The azimuth will be the most significant position. During rendering, the graphic subsystem converts the color table.