3-3 Generation of Contour Lines

Contour lines are one of the terrain features which represent the relief of the terrain with the same height.

There are two types of contour lines in visualizing GIS data; vector line drawing and raster image.

Vector Line Drawing
In case when the terrain points are given in grid, the simplest method is to divide the square cell into two triangles mechanically as shown in Figure 3.6 a and b. However such mechanical division will cause some inconveniences in smoothness of the contour lines. Figure 3.7 shows strategic division, which makes triangles depending on the slope.

In case when the terrain points are given randomly, TINs will be created as described in 3-2 (see Figure 3.6).

Raster Image
Contour image with painted contour terraces, belts or lines instead of vector lines will be generated in raster form.

In case of grid, highly densed subgrid points will be generated and the interpolated height values, which are simply sliced into contour interval are assigned to the corresponding color as shown in Figure 3.8 (a). In case of irregularly spaced points, two-step interpolation, that is coarse grid and then dense subgrid will be applied as shown in Figure 3.8 (b). The procedure is known as densification.