Use a shared-space layout for local time-point extrema

Choose a shared-space layout when readers must identify which series is highest at one time point across several time series. For example, use a simple line graph or braided graph instead of per-series rows such as small multiples or horizon graphs for a highest-at-a-time-point comparison.

A shared-space layout keeps the compared values in one vertical region on a common baseline. That lets readers compare one time point directly instead of shifting their gaze between separate rows.

Mechanism: One shared plotting area reduces row-to-row eye movement for a local same-time comparison.

Evidence: Controlled comparisons of simple line, braided, small-multiples, and horizon views found the shared-space views faster than the split per-series views for the local maximum/find-extremum task, and the collated record summarizes the same shared-space advantage for this task family (Javed et al., 2010; Zeng & Battle, 2023).

Notes: The reported advantage for this task is in completion time; the structured record does not report significant accuracy pairs here.

• User Goal: Find which series has the highest value at a specified time point.
• Task: Local extremum comparison across several simultaneous time series.
• Data: Several series share the same ordered time axis.
• Chart Setting: Static, noninteractive overview view with all series visible at once.
• Audience: Readers making quick cross-series comparisons.
• Success Criterion: Faster completion on a same-time highest-value question.

Break it when: Readers must compare values at different marked time positions across series or across a long span of the display. Why: Split per-series layouts were faster for the dispersed aggregate/discrimination-style comparison task.

Sacrifice: A shared-space layout keeps overlap in one plot. Risk: Line identity and clutter can become harder to follow than in separated rows. Mitigation: Keep the shared-space layout for local same-time questions rather than dispersed cross-series comparisons.

Mistake: Keep each series in separate rows for a same-time highest-value question. Why it fails: Separate rows add vertical scanning to a comparison that can be made in one shared position.

Failure Sign: Reviewers look up and down between rows to answer one same-time highest-value question. Quick Check: Compare the current per-series-row view against a shared-space view on the same highest-at-this-time question. Stronger Test: Time a few readers on the same question in both layouts and keep the faster one.

• Replace per-series rows with one shared plot for the local comparison view.
• If a plain line overlay is hard to follow, try a braided shared-space view before returning to split rows.
• Keep the compared time point aligned in the same shared plotting region for all series.