Use an area chart when time intervals between dates are irregular
For showing shares over ordered time, use an area chart instead of a stacked column chart on irregularly spaced dates to improve fidelity and mitigate incorrect spacing of time points for readers interpreting elapsed time.
- purpose:select
- basis:heuristic
- time:ordered-time
- chart:area:use
- chart:bar:avoid
- quality:fidelity:use
- lever:chart-family
- data:temporal
advice
Keep a continuous time axis
Use an area chart instead of a stacked column chart when the gaps between dates are not equal. For example, keep the data on a continuous time axis when some date gaps span a few years and others span decades.
reason
Why the area chart is more faithful here
Irregular date gaps need a continuous scale to show elapsed time correctly. Equal-width columns do not preserve those unequal intervals.
Mechanism: The area chart can place dates at their true positions on a continuous axis, so readers see the real spacing between time points.
Evidence: The source gives unequal year intervals as a reason to use an area chart instead of a stacked column chart, because area charts have continuous scales that show dates in the right intervals while column charts do not (Muth, 2018).
context
Use when date spacing matters
- User Goal: Show shares over time while preserving the true spacing between dates.
- Task: Read change across uneven time intervals.
- Data: Temporal values with irregular gaps between dates.
- Chart Setting: A stacked column chart is being considered for a short time series with uneven spacing.
- Audience: Readers who should interpret elapsed time correctly.
- Success Criterion: The chart shows unequal intervals at unequal distances.
exceptions
Do not use when dates are few and evenly spaced
Break it when: The dates are few and evenly spaced. Why: A stacked column chart can then improve labeling and value reading.
costs
What you give up
Sacrifice: You give up some of the labeling ease of stacked columns. Risk: With only a few evenly spaced dates, the area chart can be harder to read than a stacked column chart. Mitigation: Switch to stacked columns when spacing is even and label readability is the bigger need.
mistakes
Common failure mode
Mistake: Using equal-width stacked columns for dates that are not equally spaced. Why it fails: The chart suggests equal time gaps where the data do not have them.
check
How to test the choice
Failure Sign: The draft column chart gives the same visual width to unequal date gaps. Quick Check: Compare the column chart with an area chart on a continuous axis; if the spacing changes, keep the area chart. Stronger Test: Inspect the actual date intervals before choosing the chart type.
fix
What to change
- Move the data to an area chart with a continuous time axis.
- Position dates according to their actual intervals.
- Avoid equal-width stacked columns when the time gaps are unequal.