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GRADIENT

How to calculate the gradient using a topological map

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Formula to be applied

• Gradient is an expression of the change in elevation over the distance covered along the surface.

• Gradient =

• Express gradient in the format VD:HD

Vertical difference (in height)

Horizontal distance (on the ground)

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example

Calculate the gradient of the road from the bridge at Cocoa Estate to the junction near the radio mast on the coast. (adapted from CSEC 2012 Geography CXC May/June – Qn 1(v))

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Dominica (Lesser Antilles)

Examine the contour lines that pass through each point for the heights; and use the scale to ascertain the distance

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Steps to take

• Identify the heights of the two locations

• Measure the distance in a straight line between the two points.

• OR if specified, along the route identified (e.g the road, or river, etc)

• Ensure that both the height and the distance have been expressed in the same units (i.e metres or feet)

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What do we now know?

• The height of the bridge is 65 metres• The height of the junction is 5 metres

• The measurement of the distance between the bridge and the junction is 3000 metres

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Applying the formula

•

• therefore the gradient VD:HD (60: 3000) is 1: 50

Vertical difference (in height)Horizontal distance (on the ground)

65 - 53000

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sketched

For every fifty metres (in distance) you advanced from the bridge towards the junction you would have descended one metre (in height)