Choose a graph by looking at the data first: categories, change over time, parts of a whole or two measurements. The data type points to the graph type.
This lesson is part of map and graph skills. The investigation side is covered in presenting data clearly.
Which graph matches which data?
| Data looks like | Graph | Reason |
|---|---|---|
| Separate places or groups | Bar chart | Each bar is a separate category |
| One value changing over time | Line graph | Points join to show a trend |
| Parts of one whole, adding to 100% | Pie chart | Slices show shares |
| Two measurements for each place | Scatter graph | Dots show whether they move together |
Ask two questions. Is it one measurement or two? Is the horizontal axis a category or a time sequence?
Worked example: land use in a district
This is a worked example. A district’s land is used as follows: forest 50%, farmland 30% and housing 20%.
The data is parts of one whole, so a pie chart fits. A full circle is 360°, so each angle is the share multiplied by 360.
- Forest: 50% × 360° = 180°.
- Farmland: 30% × 360° = 108°.
- Housing: 20% × 360° = 72°.
Check the total: 180° + 108° + 72° = 360°. Label each slice with its category and percentage, and give the pie a title such as “Land use in the district”.
A sentence to go with it: “Half of the district is forest, which is 20 percentage points more than farmland and 30 more than housing.”
The mistake: the wrong graph for the data
A student draws a line graph for three towns’ rainfall in one month. The line joins Town A to Town B, but nothing exists between two towns.
| Data | Wrong choice | Better choice | Why |
|---|---|---|---|
| Rainfall in three towns, one month | Line graph | Bar chart | Towns are categories, not a sequence |
| Hourly temperature at one spot | Bar chart | Line graph | Values change over time |
| Land use shares adding to 100% | Line graph | Pie chart | The data is parts of a whole |
A second common slip is a pie chart with ten tiny slices, which no one can compare. A bar chart handles that better.
Check yourself
Which graph fits each dataset: (a) monthly rainfall in one town across 12 months, (b) share of energy from five sources, adding to 100%, (c) rainfall and river discharge for 8 towns?
Answer
(a) A bar chart or a line graph. Rainfall by month is a time sequence, so a line graph shows the trend, and a bar chart is also common for monthly totals.
(b) A pie chart, since the five shares make up one whole. A bar chart would work if the slices were too small to compare.
(c) A scatter graph, with rainfall on one axis and discharge on the other, one dot per town.
What to study next
Next, see how two maps can mislead in comparing maps without confusing correlation and cause. Then try the map and graph skills practice.
The graph evidence and fair-comparison lab lets you test your choices. For a teacher to check them with you, see online one-to-one Geography tuition.