Present investigation data so a reader can see the pattern in a few seconds. That means the right chart type, honest scales and six labelling items.
This lesson sits inside geographical investigation. For choosing among bar, line and pie graphs across all topics, see choosing a graph for geographical data.
What should a clear result chart contain?
Check these six items before you hand in any graph or table.
- A title that says what was measured, where and when.
- Labels on both axes, each with its unit.
- An even scale with equal steps, starting at zero for bar charts.
- Bars or points in a sensible order, such as by place or by time.
- A key, only if more than one set of data is shown.
- The source: “collected by the student” or the name of the supplied dataset.
Worked example: litter counts
This is a worked example. Three stretches of a school field edge were counted for 10 minutes each: A had 27 pieces, B had 12 and C had 9.
Because A, B and C are separate places, a bar chart fits. Follow these steps.
- Title: “Pieces of litter counted in 10 minutes on three 20 m stretches of the school field edge, Tuesday afternoon”.
- Horizontal axis: “Stretch (A, B, C)”. Vertical axis: “Litter pieces counted in 10 minutes”.
- Scale: the highest value is 27, so the vertical axis runs from 0 to 30 in steps of 5.
- Bar heights: A reaches 27, B reaches 12, C reaches 9.
- Source: “Collected by the student.”
A one-line reading follows: stretch A had 27 pieces, which is more than twice stretch B at 12, because 12 × 2 = 24 and 27 is higher than 24.
The mistake: an axis that flatters the difference
Suppose a student starts the vertical axis at 8 to “save space”. Then C (9) looks like a tiny bar, and A (27) looks about nineteen times taller, although it is only three times larger.
| Axis choice | Height shown for C | Height shown for A | What the reader believes |
|---|---|---|---|
| Starts at 0 | 9 units | 27 units | A is 3 times C, which is true |
| Starts at 8 | 1 unit | 19 units | A is 19 times C, which is false |
Check the arithmetic: 27 ÷ 9 = 3, but 19 ÷ 1 = 19. The numbers are identical, yet the picture says something untrue.
A second common slip is a missing unit. “Litter” on the axis could be pieces, kilograms or bags, so always write the unit.
When should a table come first?
If you have fewer than five values, a table may be enough. Write the table before the graph, because it gives the graph its numbers and lets you spot a recording error early.
Keep the raw table in your work even when the graph is tidy. It is your evidence, and it shows that the counts are yours. The graph evidence and fair-comparison lab lets you practise judging whether a chart compares places fairly.
Check yourself
A student recorded air temperature at 8.00 a.m., 10.00 a.m., 12.00 noon and 2.00 p.m. at one spot. Should she use a bar chart or a line graph, and what should the horizontal axis say?
Answer
A line graph fits, because the data is one measurement changing over time and values exist between the readings.
The horizontal axis should read “Time of day” with equal gaps of 2 hours between the readings. The vertical axis should read “Air temperature (°C)”.
A bar chart would not be wrong for marking, but it hides the idea of change through the day.
What to study next
Once the data is shown well, write the honest edge of your evidence in explaining limitations without inventing observations. Then try the investigation practice set.
To have a teacher look at your own charts, see online one-to-one Geography tuition.