Use a line chart for a single value over time
For showing one value over ordered time, prefer a line chart instead of an area chart to improve readability and mitigate an unnecessary zero-baseline requirement for readers following the trend.
- purpose:select
- basis:heuristic
- task:trend
- time:ordered-time
- chart:line:use
- chart:area:avoid
- quality:readability:use
- lever:chart-family
- measure:single
advice
Switch to a line chart
Use a line chart instead of an area chart when you are showing only one value over time. For example, remove the fill from a single time series and keep a line, especially when you do not want the y-axis to start at zero.
reason
Why a single series does not need an area
A single filled area adds little that a line does not already show. The line keeps the trend readable without imposing an area-chart treatment that is harder to label and often tied to a zero baseline.
Mechanism: The line chart keeps attention on the one changing value and avoids the extra area encoding that does not help the reader with a single series.
Evidence: The source recommends considering a line chart instead of an area chart when showing one value over time, especially if the y-axis should not start at zero (Muth, 2018).
context
Use when there is only one series
- User Goal: Show how one value changes over time.
- Task: Follow a single trend.
- Data: One temporal series.
- Chart Setting: A single-series area chart is being considered.
- Audience: Readers who need a straightforward reading of the trend.
- Success Criterion: The single trend is readable without unnecessary fill.
exceptions
Do not use when the series has only a few dates
Break it when: There are only a few dates. Why: The source says a column chart can also be a better choice in that case because labeling will be better.
costs
What you give up
Sacrifice: You give up the filled shape under the line. Risk: With only a few dates, the line chart may not label as well as a column chart. Mitigation: Switch to columns when the time series is very short.
mistakes
Common failure mode
Mistake: Using a filled area for a single time series by default. Why it fails: The extra fill does not add much, and it can force a less flexible y-axis treatment.
check
How to test the choice
Failure Sign: The chart contains only one temporal series but still uses a filled area. Quick Check: Make a line-chart version and compare whether the trend reads just as well or better. Stronger Test: If you want a y-axis that does not start at zero, reject the area chart.
fix
What to change
- Remove the fill and keep the series as a line.
- If the series has only a few dates, try a column chart instead.
- Keep the area form only if the filled shape itself is essential to the message.