Use a single 24-hour bar chart to find the daily maximum
For finding the maximum in cyclic-time hourly data, use a single-view structure on bar charts to improve fidelity and mitigate wrong-half selections for non-expert readers.
- purpose:select
- basis:empirical
- task:extreme
- time:cyclic-time
- chart:bar
- structure:single-view:use
- structure:multi-view:avoid
- quality:fidelity
- lever:layout-structure
advice
Use one continuous 24-hour bar view
Use one continuous 24-hour bar chart when the task is to find the day-wide maximum. For example, merge separate AM and PM bar panels into one 24-hour axis instead of asking readers to scan two 12-hour charts for the highest bar.
reason
Why one continuous view works
A continuous bar view lets readers scan one run of bars and judge the global maximum without switching panels. Split views force a cross-panel search and can make readers pick the highest bar from the wrong half of the day.
Mechanism: One uninterrupted sequence reduces panel switching and supports a direct search for the tallest bar across the full day.
Evidence: For the daily-pattern maximum task, the 24-hour linear bar chart was the fastest condition, and split charts produced errors where readers selected the maximum from the wrong chart half (Waldner et al., 2020; Zeng & Battle, 2023).
context
Use when the maximum must be found across the whole day
- User Goal: Identify the highest hour in the full 24-hour cycle.
- Task: Find the global maximum.
- Data: One value per hour across a single day.
- Chart Setting: Bar chart shown either as one 24-hour view or as separate AM/PM panels.
- Audience: Non-expert readers.
- Success Criterion: Fast and correct selection of the day-wide maximum.
exceptions
When to break the rule
Break it when: The available width cannot support a readable 24-hour bar chart. Why: The supported fallback is to keep the display linear and split it into separate bar panels rather than switching to a rose chart.
costs
What you trade away
Sacrifice: You lose the smaller AM/PM chunks that can make each half feel locally simpler. Risk: If the 24-hour chart is squeezed too tightly, bars can become crowded. Mitigation: Use split linear panels only as a fallback when the continuous 24-hour view does not fit.
mistakes
Common failure mode
Mistake: Keeping separate AM and PM panels when the reader must find the day-wide maximum. Why it fails: Readers can stop at the maximum in one panel and miss that the higher bar is in the other panel.
check
How to test the choice
Failure Sign: Readers report the maximum from AM or PM without checking the other half. Quick Check: A/B test a 24-hour bar chart against split AM/PM bar charts on one maximum-finding question. Stronger Test: Record completion time and note whether wrong answers come from choosing the tallest bar in the wrong panel.
fix
What to change
- Merge AM and PM panels into one 24-hour bar chart for the maximum-finding view.
- Keep one continuous hourly axis so the tallest bar is searched in a single scan.
- If the chart cannot fit at full width, use split linear bar panels as the fallback rather than a radial chart.