The line X-Y on the map of the Canary Islands, right, indicates the line of a cross-section. An elevation profile of the line X-Y is also shown.
1. Name the island at A on the elevation profile.
2. What is the depth of the ocean at B on the elevation profile?
3. Calculate the difference in elevation between point C and point D on the profile to the nearest 1000 m.
) Fig. 14.12 (a) A map of the Canary Islands and (b) a cross- section (0 represents sea level)
(b)
1000 3000
2000 m 0
–1000 –2000
–5000 –4000 –3000
0 Atlantic Ocean La Palma Tenerife Fuerteventura La Gomera El Hierro Gran Canaria Lanzarote
Map of Canary Islands
100
200 km
300
400
500
Skill 8: Calculating Average
Gradient Average gradient is the ratio between distance travelled and change in height. If a person walked for 1 km and the height changed by 10 m, we can figure out the average change in gradient (slope):
1000 m 10 m
= 100 m
therefore for every 1 m change in height a person has to walk a distance of 100 m. So how do we calculate it?
We use the following formula: Average gradient (AG) =
Vertical interval (VI) (the difference in height between the two points) Horizontal equivalent (HE) (the distance travelled)
GEO NUMERACY
Using Fig. 14.13, calculate the average gradient between the triangulation point of Crohaun Mountain S 275 005 to the spot height at S 298 001.
AG = VI = 484 m – 154 m = 330 m = 1 = 1:7.3 HE
2.4 km 2400 m 7.3
Therefore for every 7.3 m you walk, the height changes by 1 m.
