What is a cross section?
It is a side view of a specific land form/topography.
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| Example of a cross section |
Lets say you must draw a cross section between two points on a topographic map e.g. from spot height 1463 to trig beacon 159.
Step 1: Draw a line between spot height 1463 and trig beacon 159
Step 2: Place a piece of paper on the line connecting the two points and mark the spot height and trig beacon positions on the piece of paper
Step 3: Mark every contour line crossing the line (piece of paper) and write the heights for each contour line down.
Step 4: Draw a graph with an X and Y axis. On the vertical axis use a scale e.g. 1cm represents 20m. The first height on the vertical axis will be the lowest height of the contour lines and last height the height of the highest spot height / trig beacon.
Step 5: Transfer the markings on the piece of paper onto the horizontal axis.
Step 6: Plot the heights for each contour line and connect them with a line.
Step 7: Finalise the cross section by labelling it and shade the area below the line graph.
How to calculate vertical exaggeration
When you have done a cross section, the height and gradient of features on the cross section may be distorted. It can appear much steeper, narrower and higher than in reality. The vertical exaggeration shows you by how much the vertical scale has been distorted. Five times is a relatively good representation, however, an exaggeration bigger than five times become to distorted.
The vertical scale chosen will therefore have a huge impact on the distortion of the cross section. Let’s use a scale of 1cm represents 20m. You first need to convert the word scale into a fraction scale.
Now the vertical scale is the same as the horizontal scale e.g. 1:50 000
Use the following formula to calculate the vertical exaggeration –
Intervisibility
Intervisibility is the ability to see one point from another point on the landscape.
The motor car at B is not intervisible from the man on the hill, but the motor car at A is intervisible. On a cross section draw a straight line with a ruler to see if the topography intersects that line. If not, there will be intervisibility.
