Contour lines

1. Contour lines

2. Contour lines: curved lines drawn on the map, connecting points having the same elevation

3. Contour interval: is the vertical distance between successive contour lines • Example: 0.5m, 1m, 2m, 5m, 10m, 20m, 50m • Contour interval should not be changed over the same map (constant over the same map) • interval=5m 15 10 5

4. Factors that decide the contour interval • 1- the area topography: flat area… small interval • 2- the scale of the map: • Small scale maps……..large intervals • 3- purpose of the map • Engineering construction over small site……small contour interval

5. Characteristics of the contour lines • 1- continuous closed curved lines • 2- cannot meet or cross any other contour lines • 3- cannot split or join any other lines except in the case of a cliff

6. 4- close to each other at steep slopes • 5- wide spacing between contour lines at flat slopes

7. 6- uniformly spaced contours indicates uniform slope • 7-contour lines at a river valley take a V shape pointing to the river source (upstream) upstream

8. River valley

9. Methods of contour line measurements and plot • 1- grid method: divide the area into equal size squares (grid) and measure the elevations at each corner • 2-Spot height method: measure the elevations and coordinates of points(not regularly spaced) that best represent the shape of earth surface • 3-Cross section method: use the data of the profile and cross section to plot the contour lines

10. Grid method • Example data for simple grid • x, y, elevation data for 50x50m grid • 0,0,60 • 0,100,55 • 100,100,58 • 100,0,75 • 50,50,80

11. contour map generated by surfer program (2m interval)

12. Fill contour map

13. Wireframe map

14. Vector map

15. new data • 0,0,60 • 0,100,55 • 100,100,58 • 100,0,75 • 80,50,120 • 100,50,60

16. On steep slopes contours are close to each other