Use a line chart when the task is to read x–y relationships
For relationship reading on quantitative x–y data, use a line chart instead of a bar chart to improve readability and mitigate misreading of x–y structure for readers interpreting standard charts.
- purpose:select
- basis:empirical
- task:relate
- chart:line:use
- chart:bar:avoid
- quality:readability:use
- lever:chart-family
advice
Choose the chart family for relationship reading
Use a line chart when readers need the relationship between x and y. For example, replace a bar chart with a line chart when the main readout is the pattern across x-values rather than side-by-side comparison of nearby magnitudes.
reason
Match the chart to the reading task
A line chart makes the coordinate relationship easier to trace across x-values. That direct path helps readers read the relationship itself instead of recasting each x-position as an isolated bar.
Mechanism: Connecting values into a continuous x–y path supports relationship reading more directly than separate bars.
Evidence: Line graphs facilitate extraction of information for x–y relationships, while bar graphs better support comparison of graphical elements in close proximity (https://doi.org/10.1073/pnas.1807180116">Börner et al., 2019).
context
Use when the main question is about the relationship across x and y
- User Goal: Explain or inspect how one quantitative measure relates to x-values.
- Task: Read the x–y relationship rather than compare nearby magnitudes.
- Data: Quantitative values arranged on x and y.
- Chart Setting: You are deciding between a line chart and a bar chart for the same data.
- Audience: Readers interpreting a standard chart.
- Success Criterion: Readers can correctly read the relationship across x and y.
exceptions
Do not use when the main task is local magnitude comparison
Break it when: The main task is comparing graphical elements in close proximity. Why: Bar graphs better support that comparison task.
costs
Accept the tradeoff in local comparison
Sacrifice: Ease of comparing nearby magnitudes one by one. Risk: Readers may have to work harder if the real question is which nearby value is larger. Mitigation: Use the line chart only when the relationship across x and y is the primary readout.
mistakes
Avoid the wrong chart family for the task
Mistake: Keeping a bar chart when the intended readout is the x–y relationship. Why it fails: Readers must interpret separate bars instead of following the relationship directly.
check
Test the task against both chart families
Failure Sign: Reviewers answer local bar-height questions easily but struggle to describe the relationship across x and y. Quick Check: Make a line version and a bar version of the same data, then ask which one more directly answers a relationship question. Stronger Test: Ask a reviewer to read the x–y relationship from both versions; keep the line chart if the relationship is easier to extract.
fix
Replace the chart family, not the data
- Replace the bar chart with a line chart for the same x and y variables.
- Keep the underlying values the same so the main change is the chart family.
- If reviewers actually need nearby magnitude comparison, switch back to a bar chart.