On a topographic map, index contours are drawn at elevations of 400\text{ m} and 700\text{… — JAMB UTME

On a topographic map, index contours are drawn at elevations of $400\text{ m}$ and $700\text{ m}$ . There are $5$ equal contour intervals (spaces) between these two index contours. A radio transmission mast is located on a contour line situated $3$ contour intervals higher than the $700\text{ m}$ index contour. What is the elevation, in meters, of the contour line where the radio mast is located?

Answer: 880 m

Answer

The elevation of the contour line where the radio mast stands is

880\text{ m}

The elevation difference between the

400\text{ m}

and

700\text{ m}

index lines is

300\text{ m}

. With

5

equal spaces separating them, the contour interval is

60\text{ m}

. Adding

3

contour intervals (

180\text{ m}

) to the

700\text{ m}

index line yields an elevation of

880\text{ m}

Step-by-Step Solution

Calculate the elevation difference between the given index contours.

Vertical difference =

700\text{ m} - 400\text{ m} = 300\text{ m}

Index contours serve as reference lines to determine the vertical rise across intervening contour spaces.

Determine the contour interval (the vertical distance between consecutive contour lines).

Contour Interval =

\frac{300\text{ m}}{5} = 60\text{ m}

Dividing the total height difference between index lines by the number of spaces gives the value of a single contour interval.

Calculate the target elevation at 3 contour intervals above the

700\text{ m}

index line.

Target elevation =

700\text{ m} + (3 \times 60\text{ m}) = 880\text{ m}

Adding three vertical intervals (

180\text{ m}

) to the

700\text{ m}

reference line gives the exact height of the target contour line.

Key Concept

Contour Interval Determination and Relief Elevation Calculation

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