Height is shown in four different ways on a map: • Contour lines • Colour
• Spot heights • Triangulation stations/pillars
Contour Lines • Contour lines mark areas of equal heights above sea level. • They are usually drawn at intervals of 10 m.
• Index contours represent 50 m intervals (they are darker and thicker) and are always numbered.
Colour Layers • Seas are shown in light blue. • Land that lies between 0 m (sea level) and 100 m is shown in dark green. • Land between 100 m and 200 m is shown in light green. • Land between 200 m and 300 m is shown in cream. • Land above 300 m is shown in brown. • The higher above 300 m the land is, the darker the shade of brown it is.
Spot Height
• Round black spots are used tell the exact height of an area in metres.
Triangulation Stations or Pillars
• Triangulation stations or pillars are points on the top of hills and mountains where the exact height has been measured.
• These points are represented by a black triangle with the height written beside it in metres.
• Triangulation points that are not filled with black mark the highest point on the map.
Skill 6: Identifying Slope
We can identify different slope patterns by looking at contour line patterns. The more tightly packed contour lines are, the steeper the slope. The more widely spaced contour lines are, the more gentle the slope is. If an area of land is flat, there are no contour lines as the height does not change. There are four basic types of contour line:
• Even slopes can be identified on a map by their evenly spaced contour lines. They are sometimes referred to as regular slopes.
: Fig. 14.9 Can you identify the different slopes visible on this OS map extract?
GEOGRAPHICAL SKILLS 261
: Fig. 14.8 Spot heights and triangulation pillars on Peakeen Mountain
GEO DICTIONARY
Contour lines: black lines on a map that join places of equal height
Spot heights: black dots that give the exact height of ground in metres
Triangulation stations: triangles that appear on top of hills which show the height in metres
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Being able to accurately tell the height of an area also allows you to determine what landscapes can exist in that area, e.g. upland areas are where
