Relief is the shape and height of the land. Topographic maps show relief in several ways so we can picture the landscape.
Ways of showing height
- Contour lines: lines joining all points of equal height above sea level. The gap in height between two contours is the contour interval.
- Spot height: a dot with a number giving the exact height at that point.
- Trigonometrical (trig) station: a surveyed point marked with a triangle and its height.
- Layer tinting: bands of colour for different height ranges.
Key idea
Contours placed close together mean a steep slope; contours placed far apart mean a gentle slope. A contour never joins points of different height.
Cross-section
A cross-section is a side view of the land drawn along a chosen line. To draw one: lay the edge of a paper along the section line, mark where each contour crosses and note its height, then plot these heights on a graph with a horizontal distance axis and a vertical height axis, and join the points with a smooth curve.
Example
Where the vertical scale is stretched more than the horizontal scale, the profile shows vertical exaggeration, making hills look steeper than they really are.
Gradient
Gradient measures steepness and is found by dividing the vertical rise by the horizontal distance, giving a ratio such as 1:20.
Remember
- A contour joins points of equal height.
- Close contours = steep; wide-spaced contours = gentle.
- Gradient = vertical rise ÷ horizontal distance.