• Mark the y-axis in metres above sea level and write a suitable scale, e.g. 2 cm = 100 m increase in height (one full graph paper box is 100 m up).
• Place your sheet of paper straight along the x-axis and mark in all of your points from start to finish (your starting point is where the x-axis and y-axis meet).
• Plot your heights on the graph paper and join them in a smooth curve (do not use a ruler to join them). (b)
• Mark in any important features such as roads, rivers and lakes.
• Mark the six-figure grid references of your start and end points on the x-axis.
• Add the title of your cross-section (e.g. Cross-section Across Peakeen Mountain).
• Calculate the vertical exaggeration. Because we have to squash such a large area into such a small graph, increases in slope look much bigger than they are in real life. This is called vertical exaggeration. We can figure out by how much slopes have been exaggerated using a simple formula which is shown in the Geo Numeracy box.
(a) 100 500 Tributary 400 Cross-Section Across Peakeen Mountain 600
Peakeen Mountain
300
The Kerry Way
200
Cummeenboy River
Tributary
Vertical exaggeration is I0
: Fig. 14.11 (a) An extract of the OS map of Kenmare (Fig. 14.20 on page 270) and (b) a cross-section of the map extract
GEO NUMERACY To calculate vertical exaggeration, do the following: The normal scale for distance on OS maps is 2 cm = 1 km, i.e. 2 cm = 1000 m
The scale written for height (y-axis) is up to you, but I suggest making every full graph box equal 100 m, i.e. 2 cm = 100 m.
Therefore, to find out by how much our height is exaggerated on the graph, we divide the x-axis scale by the y-axis scale:
Horizontal scale (HS) = 2 cm = 1000 m Vertical scale (VS)
2 cm = 100 m Therefore the vertical exaggeration is 10.
