Use a line chart when differences between values are very small
For comparing multiple values over ordered time, prefer a line chart on temporal series instead of an area chart to improve fidelity and mitigate hidden small differences for readers who need to see subtle change.
- purpose:select
- basis:heuristic
- task:compare
- time:ordered-time
- chart:line:use
- chart:area:avoid
- quality:fidelity:use
- lever:chart-family
advice
Switch to a line chart
Use a line chart instead of an area chart when the differences between values are very small. For example, redraw small gaps as lines and allow a tighter y-axis range instead of forcing a zero-based area chart.
reason
Why the line chart reveals small gaps
Area charts usually need a zero baseline, which compresses small differences. A line chart can use a tighter y-axis range, so subtle separations stay visible.
Mechanism: The line chart can stretch the y-axis to show tiny differences that disappear when an area chart starts at zero.
Evidence: The source says area charts work best for considerably large differences, and recommends a line chart when differences are very small because the y-axis of a line chart does not need to start at zero (Muth, 2018).
context
Use when subtle differences are the message
- User Goal: Show small differences between values over time.
- Task: Compare closely spaced series or small changes.
- Data: Multiple temporal values with only slight separation.
- Chart Setting: An area chart is under consideration for a time series.
- Audience: Readers who need to detect subtle differences.
- Success Criterion: Small differences remain visible in the chart.
exceptions
Do not use when differences are already large
Break it when: The differences between the values are considerably large. Why: The area chart can then show the trends well enough without hiding the message.
costs
What you give up
Sacrifice: You give up the filled part-to-whole look of the area chart. Risk: The chart no longer emphasizes the total as a stacked shape. Mitigation: Use the line chart only when the small differences themselves are the key message.
mistakes
Common failure mode
Mistake: Keeping an area chart even though the important differences are tiny. Why it fails: The zero-based area scale compresses the variation that readers need to see.
check
How to test the choice
Failure Sign: The series look nearly flat or merged in the area chart even though their differences matter. Quick Check: Make a line-chart version with a tighter y-axis and compare whether the small differences become legible. Stronger Test: If the important gaps only become visible after removing the area fill and zero-baseline constraint, reject the area chart.
fix
What to change
- Replace the area chart with a line chart.
- Use a y-axis range that shows the small differences clearly.
- Keep the area chart only if the differences are large enough to stay visible.