Provide an alternative view for difficult charts

Add a companion or switchable alternative view when a chart type is difficult or complex. For example, let users switch a pie chart to a stacked bar, add discrete marks to a line chart, and divide a bar into countable isotypes when those edits preserve the same analytical task.

Alternative views lower the amount of interpretation work the reader must do when a chart type is hard to parse. Keeping the same task available in a more accessible presentation lets the reader continue the analysis without losing the question the chart is meant to answer.

Mechanism: An alternative presentation changes the form of the data display, not the analytical goal, so readers can move to a chart or mark treatment that is easier for them to interpret.

Evidence: Chartability recommends that difficult or complex charts be adjustable into more accessible alternatives that still accomplish the same analytical task, and it identifies pie charts, line charts without discrete marks, and bar charts without countable isotypes as cognitive risks (Elavsky et al., 2022). Research on accessible data visualization for people with intellectual and developmental disabilities supports avoiding pie charts, using discrete marks or countable pictograms, and allowing readers to switch between representations that match their cognitive needs (Wu et al., 2021; State of the States IDD Demo – CU VisualAB, n.d.).

Notes: The alternative can be shown alongside the original chart or exposed through a user control.

• User Goal: Interpret a chart that may be difficult to read accurately.
• Task: Keep the same analytical task available after the presentation changes.
• Chart Setting: The chart is difficult or complex, or it uses a high-risk form such as a pie chart, a line without discrete marks, or a bar without countable isotypes.
• Audience: Readers with cognitive accessibility needs.
• Success Criterion: The reader can move to an easier-to-interpret view without losing the intended task.

Break it when: the chart is not high risk for cognitive difficulty, or the alternative presentation no longer supports the same analytical task. Why: the source limits this guidance to difficult charts and requires the alternative to preserve the task.

Sacrifice: You add another presentation or a control for switching views. Risk: The alternative can fail if it changes the chart’s question instead of only changing the presentation. Mitigation: Keep the data and analytical task constant across views.

• Mistake: Leave a difficult chart type as the only available view. Why it fails: Readers who struggle with that form have no accessible way to perform the task.
• Mistake: Add a second chart that changes what the reader is supposed to analyze. Why it fails: The source requires the alternative to accomplish the same analytical task.

Failure Sign: A pie chart, a line without discrete marks, or a bar without countable isotypes is shown with no companion view or switchable alternative. Quick Check: Verify that the user can open or view a different presentation of the same data for the same task. Stronger Test: Try to answer the same analytic question in the alternative view; if the task changes or no alternative exists, fail.

• Add a switch that changes a pie chart into a stacked bar while keeping the same comparison.
• Add discrete marks to a line chart so intervals are shown as distinct positions.
• Divide a bar into countable isotypes when counting units helps interpretation.
• If switching is not available, place the alternative chart alongside the difficult chart.