Contour lines

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

• 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

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

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

• 4- close to each other at steep slopes

• 5- wide spacing between contour lines at flat slopes

• 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

River valley

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

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

contour map generated by surfer program (2m interval)

Fill contour map

Wireframe map

Vector map

new data

• 0,0,60• 0,100,55• 100,100,58• 100,0,75• 80,50,120• 100,50,60

On steep slopes contours are close to each other