CHAPTER 12: OS MAPS AND AERIAL PHOTOS (d) Trigonometrical stations/triangulation stations
These fulfil the same role as spot heights except they are marked as open triangles on the map with the height written beside them. They are located on specific places which were important to surveyors in the past. The surveyors built a pillar to hold surveying equipment at the point marked. These stations usually show the highest peaks in a mountain range and have had further importance to communication systems in the country as TV, radio and phone masts are often constructed at these points.
MAP SKILLS EXERCISE
Look at Fig. 16 on page 220. Name and locate an example of each method used to show height on this OS map.
7. Slope Contour lines can be used to work out the shape of the land, e.g. gentle slopes, steep slopes. They also show the shapes of river, marine and glacial landforms such as V-shaped valleys, cliffs and corries.
ed/uniform slope
graded/uniform slope
Concave slope
Concave slope
Even/graded/uniform slope Fig. 18 Slopes and contour lines even
Concave slopes have a steep upper section (contour
lines close
together) and a gentle lower section (contour lines widely spaced). Convex slopes have a gentle upper section (widely spaced contours) and a steep lower section (contour lines are closely packed together). Even, graded or uniform slopes have contours that are spaced evenly. Stepped slopes have contours that show a combination of flat and steep sections. Steep slopes have contours that are close together. Gentle slopes have contours that are quite far apart.