ACTIVITY 2.5 Calculating gradient (Individual) Refer to the topographic map extract 2528CA Pretoria on pages 4 and 5 . 1. a. Calculate the gradient of the slope from spot height 1357 (block H2) to the bench mark 1267.8 (block H2). b. State whether this gradient is gentle, moderate or steep. (2) 2. a. Calculate the average gradient between trig beacon 120 (block D5) and spot height 1217 (block D3). b. Explain why the slope of the land here was important in the development of the Wonderboom Airport. (2) [12] Check your answers against those given to you by your teacher, and make corrections to your work if necessary.

Below is one sample worked‐example showing one way to solve the problem. (Note that the exact numerical answers depend on the horizontal distances you measure on the map. Your teacher’s answer may use the same measured distances. The ideas and method below are what you should reproduce.) ────────────────────────────── Example for Question 1 1(a). To calculate the gradient along a slope, use   gradient = (vertical difference ÷ horizontal distance) × 100%                         (“% gradient”) Step 1. Find the vertical difference.   Elevation at spot height = 1357 m   Elevation at bench mark = 1267.8 m   Vertical drop = 1357 – 1267.8 = 89.2 m Step 2. Determine the horizontal distance.   Using the grid on block H2 on the map extract, you may measure—for example—a distance of 800 m along the slope.   (When you work this problem, use your map’s scale and grid to find the exact distance.) Step 3. Calculate the gradient.   Gradient = (89.2 m ÷ 800 m) × 100% = 11.15%   You might express this as “approximately 11%.” 1(b). Classification of gradient:   A gradient of about 11% means that for every 100 m horizontally there is an 11‐m change in height.   For many purposes a slope around 10–12% is regarded as moderate.   Therefore you can state that the slope is moderate. ────────────────────────────── Example for Question 2 2(a). Again use the gradient formula.   gradient = (vertical