Rule #1- Contour lines never cross. All points along a contour line represent a single elevation.
Rule # 2- Contour lines form closed circles around the tops of hills and mountains.
Rule # 3- Contour lines form closed circles marked with short, straight lines (hachure marks) inside the circle around depressions.
Rule # 4- Contour lines that cross a valley or stream are V-shaped.
Rule # 5- The spacing of contour lines depends on slope characteristics.