5 Rules of Contour Lines

1. Contour lines never intersect or cross one another

2. Contour lines curve in an upstream direction when they cross a stream valley.

3. Every contour line should eventually meet itself, either inside or outside the map area.

4. Where contours are spaced close together, the topography is steep; where they are far apart the slopes are gentler.

5. Hachured contours indicate a depression.

Gradient = Elevation Difference / Horizontal Difference