The purpose and structure of triangular graphs

Triangular graphs are a specialised type of chart used to display data that is divided into three components, where the total always adds up to 100%.

Key features of triangular graphs

• Three axes - Each side of the triangle represents one category, with a scale typically ranging from 0 to 100%.
• Percentage data - The graph is designed for data sets where the sum of the three components equals 100%.

How to read data from triangular graphs

Reading a triangular graph involves identifying the value of each category at a specific point within the triangle.

Steps to read a triangular graph

1. Locate the point - Identify the specific point on the graph that represents the data you want to read.
2. Rotate for clarity - Turn the graph so that one axis (set of numbers) is facing you the right way up. Trace the line from the point straight across to this axis and note the value.
3. Repeat for other axes - Keep turning the graph for each of the other two axes, following the same process to record the values for the remaining categories.
4. Verify the total - Ensure the three values you've recorded add up to 100%.

Example of reading a triangular graph

Consider a point on a triangular graph representing population distribution by age. Following the steps:

• For the axis labelled "% Aged under 30 years", the line from the point reads 50%.
• For the axis labelled "% Aged 30-60 years", the value is 30%.
• For the axis labelled "% Aged over 60 years", the value is 20%.

Double-check the total: 50 + 30 + 20 = 100%. This confirms the reading is correct.

How to plot data on triangular graphs

Plotting data on a triangular graph requires precision to ensure the point accurately represents the proportions of the three categories.

Steps to plot data on a triangular graph

1. Start with the first category - Rotate the graph so the axis for the first category is facing you the right way up. Locate the value for this category on its axis and draw a faint pencil line straight across the graph.
2. Repeat for the other categories - Do the same for the other sets of numbers, turning the paper round each time.
3. Find the intersection - Where your three lines meet, draw a dot.
4. Double-check accuracy - Verify that the dot is in the correct place by following the steps for reading triangular graphs.