What this lesson teaches
I can read and choose the right maps, graphs, photographs and other visual resources.
Syllabus 8834, Fieldwork, Additional Notes on Data. Students are required to be familiar with the following types of data: Maps: contour maps, choropleth maps, isoline maps, dot maps, flow-line maps, proportional symbols maps and cartograms; Graphs: pie charts, bars, histograms, scatter graphs, radar charts, triangular graphs and line graphs; Photographs: landscape photographs, aerial photographs and satellite images; Others: tables, schematic diagrams, illustrations and cartoons.
Make a guess
A point on a triangular graph shows 30% walking and 50% public transport. What share is private transport?
- 80%, because it is the rest of public transport.
- 50%, the same as public transport.
- You need a third reading from the graph.
- 20%.
Show the answer
20%.
The three shares are parts of one whole and add up to 100%. So 100 minus 30 minus 50 leaves 20%.
Each corner of a triangular graph means 100% of one part, and lines parallel to the opposite side show that part's share.
A triangular graph shows how one whole splits into three parts. The shares must use the same total, not overlap, and add up to 100%. Our example shows each resident's main way of travelling: walking, public transport or private transport.
At the walking corner, walking is 100% and the others are zero. On the opposite side, walking is zero. A line parallel to that side shows a fixed walking share. Use the same rule for the other two corners. Follow the labelled direction of each scale.
To plot point A, use 30% walking and 50% public transport. Their lines meet at one point. Check the third share: 20% private transport. Only two values are needed, because all three add to 100%.
Moving towards a corner means that part's share rises. A change in share does not show a change in numbers of people.
- Corner
- 100% of one part.
- Parallel lines
- Show a fixed share of one part.
- Rule
- The three shares must add to 100%.
Step by step
Check the whole
Three parts of one total, no overlap.
Follow the parallel lines
Find two shares.
Check the third
It should make the total 100%.
Worked example: Check before plotting
Shares of 40%, 35% and 25% make one point. Shares of 40%, 50% and 30% cannot, because they add to 120%. Check for overlapping categories or a different total.
Watch out for this
A triangular graph can compare any three percentages.
It shows three parts of one whole. Unrelated percentages do not belong on it.
Check your understanding
Walking is 25% and public transport is 45%. What is private transport, if these are the only three modes?
- 30%.
- 70%.
- 20%.
Show the answer
30%.
Yes. 100 - 25 - 45 = 30.