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

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, ,50,60

On steep slopes contours are close to each other