IGCSE Geography / Economic activity and energy

Reading and plotting triangular graphs

Edexcel International GCSE Geography (4GE1), chapter 4: Economic activity and energy, specification point 4.1a, 4.S1. Free lesson.

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A triangular graph shows three percentages that add up to 100, such as the shares of workers in different sectors. You can use it to read or plot values and compare how developed countries are.

What the three scales show

Each side of a triangular graph is a scale from 0 to 100. The point represents three percentages, so the values must add up to 100. In this example, the percentages show the share of workers in each sector. Tertiary includes quaternary jobs. Primary means jobs such as farming. Its scale is on the left. Secondary means making things. Its scale is along the base. Tertiary means services. Its scale is on the right.

How to read a point

Follow the lines for each scale to read its percentage. Do not use the same direction for all three. The tick marks lean the same way as the lines you should follow to that scale. Ethiopia has about 60% of workers in primary jobs, so its point is towards the primary corner. China has 22% primary, 32% secondary and 46% tertiary. Its point is near the middle. The UK has 83% in tertiary jobs, so its point is near the tertiary corner.

How to avoid reading the wrong lines

A common mistake is to read straight across for every scale. Straight across gives the tertiary value, not the primary value. If your three readings do not add up to 100, check that you followed each scale's own lines. For China, the correct readings are 22% primary, 32% secondary and 46% tertiary. The incorrect primary reading of 54% comes from using the tertiary line. The incorrect readings total 132%, which cannot represent one workforce.

How to plot a point

Plotting is reading a triangular graph in reverse. Two percentages locate the point where their lines cross. Use the third percentage to check that the point is correct. The UK in 2025 is near the tertiary corner. For the UK in 1901, the values were 13% primary, 44% secondary and 43% tertiary. They add up to 100.

What a point's position suggests

A country's position can show how its employment structure changes as it develops. A point near the primary corner suggests a less developed country. Over time, it tends to move away from primary and towards tertiary. The UK is developed. Machines do most farm work, so few workers are needed in farming and most people work in services. Ethiopia is developing. Farming still needs many workers, with about 60% in primary jobs, compared with about 1% in the UK.

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