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
In a survey, 12 of 20 residents walk. What angle should the walking sector have on a pie chart?
- 12 degrees, one for each walker.
- 216 degrees.
- 60 degrees, the same as the percentage.
- 180 degrees, because most people walk.
Show the answer
216 degrees.
12 divided by 20 is 0.6, or 60%. Multiply by 360 to get 216 degrees.
A pie chart splits one whole into parts, and the angles must add up to 360 degrees.
First find the total. This chart shows the main way 20 residents travel. Each person picks one category, so walking, public transport and private transport are separate parts of one whole.
Divide each count by the total. Walking is 12 / 20 = 60%. Its angle is 0.6 x 360 = 216 degrees. Public transport is 30%, or 108 degrees. Private transport is 10%, or 36 degrees. Draw each sector with a protractor from a starting line, then add a key.
Check the shares add to 100% and the angles to 360 degrees. Show the sample size: 60% of 20 is fewer people than 40% of 100. A small sample may not represent the whole neighbourhood.
If people can choose several ways to travel, answers overlap. Use a bar chart instead. Or define one main way of travel per journey before drawing a pie.
- Share
- Count divided by total.
- Angle
- Share times 360 degrees.
- Check
- Shares total 100%; angles total 360 degrees.
Step by step
Check the total
Categories must not overlap.
Work out each angle
Count divided by total, times 360.
Draw and check
Protractor, key, and a 360-degree total.
Worked example: One share, two forms
Six of 20 residents mainly use public transport. That is 6 / 20 = 30%, or 6 / 20 x 360 = 108 degrees. The percentage and angle show the same share.
Watch out for this
A bigger percentage always means more people.
It depends on the total. Compare sample sizes first.
Check your understanding
What angle shows 25% of a pie chart?
- 25 degrees.
- 90 degrees.
- 180 degrees.
Show the answer
90 degrees.
Yes. 0.25 x 360 = 90.