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
You recorded route distance and journey time for 20 journeys. Which graph shows whether the two are linked?
- A line graph joining the journeys in order.
- A bar chart of each journey's distance and time.
- A scatter graph, one point per journey.
- A pie chart of the journey times.
Show the answer
A scatter graph, one point per journey.
A scatter graph pairs two measurements from the same case, so you can see whether longer routes go with longer times.
Choose a graph after deciding what the numbers represent and what comparison matters.
Bar charts compare separate categories. Start the scale at zero. Pie charts show parts of one whole, adding up to 100%. For example, 12, 6 and 2 journeys out of 20 are 60%, 30% and 10%, or 216, 108 and 36 degrees.
Line graphs show change in order, usually over time. Label the units and intervals. Joining points suggests a trend, but does not prove what happened between readings. Space times evenly only if they are evenly spaced. When gaps between readings differ, use a numbered time axis.
Scatter graphs pair two variables from the same case to show a relationship. Do not join the points like a time series. Describe the overall pattern and exceptions.
Tables keep exact values and can show many variables. Give clear headings, units and sample sizes. Avoid cut-off scales or decorations that exaggerate differences. Graphs make patterns easy to see; tables make exact checking easy.
- Bar chart
- Compare separate categories.
- Line graph
- Show change in order, often time.
- Scatter graph
- Show a relationship between two variables.
Step by step
Find the comparison
Categories, whole, sequence or pairs?
Draw and label
Scale, title, units, key, source and date.
Check the meaning
Is anything hidden or falsely linked?
Worked example: A misleading pie chart
Residents may use both buses and walking. A pie of these overlapping answers is wrong, because they are not parts of one whole. Use a bar chart instead, noting that people could pick more than one.
Watch out for this
Any percentages can go in a pie chart.
The categories must be parts of the same whole, with no overlap.
Check your understanding
Which graph best shows the link between route distance and journey time for 20 journeys?
- A scatter graph with one point per journey.
- A pie chart of the distances and the times.
- A line joining residents in name order.
Show the answer
A scatter graph with one point per journey.
Yes. It pairs the two variables for each journey.