Provide 24×24 px pointer targets or an alternative interaction path

Make each pointer-activated interaction target at least 24×24 px, or add a separate interaction path that reaches the same information and task when the visible mark cannot be enlarged. For example, keep a data-scaled mark visually small if size encodes data, but add a minimum-size text label, an accompanying data table or search control, or a keyboard, zoom, or filter path that lets users select or activate the same item.

Small pointer targets demand precise motor control. Minimum-size targets or a parallel interaction path let users select, activate, or inspect the same information without depending on fine pointer accuracy.

Mechanism: Larger or alternate targets reduce the precision required to hit a mark and make the same represented item reachable through a more tolerant control path.

Evidence: Pointer-activated controls should be at least 24×24 px, and when data-scaled marks cannot meet that size the chart should provide another way to select, activate, or interact with the same information or task; supported alternatives include labels, tables, search, keyboard input, zooming, and filtering, while Voronoi-style overlays alone may still leave motor barriers (Elavsky et al., 2022; W3C, n.d.).

• User Goal: Select, activate, or otherwise interact with a represented item.
• Task: Reach a specific mark or trigger an item-level action.
• Data: The chart uses small interactive elements, including marks whose size is mapped to data values.
• Chart Setting: Mouse or touch pointer interaction is offered.
• Audience: People with motor impairments, people using non-precise touch input, or users who need an alternative to precise pointing.
• Success Criterion: The same represented item can be reached and operated without fine pointer precision.

Break it when: The visible mark size is itself a data encoding and enlarging the mark would change what the chart means. Why: Changing the visible mark would distort the encoding, so the repair must be a separate interaction path instead.

Sacrifice: Larger targets or parallel controls take extra interface space or implementation work.
Risk: Hidden target-expansion tricks alone can still leave substantial operability barriers.
Mitigation: Add one visible, discoverable alternative control that reaches the same represented item or task.

• Mistake: Keep tiny, data-scaled marks as the only selectable elements. Why it fails: Users must hit a very small target to reach the information or action.
• Mistake: Rely only on a Voronoi-style overlay to make marks easier to hit. Why it fails: The source notes that this can still leave significant operability barriers for people with motor impairments.

Failure Sign: An interactive mark or control is smaller than 24×24 px and no other control reaches the same information or task.
Quick Check: Measure the target area of any pointer-activated element and flag anything under 24×24 px.
Stronger Test: For any tiny or data-scaled mark, verify that the same item can also be selected, activated, or inspected through a non-precise path such as a label, table, search, keyboard path, zoom, or filtering control.

• Increase the interaction target to at least 24×24 px.
• Add a minimum-size text label that can be selected or activated instead of the tiny mark.
• Add an accompanying data table or search control that reaches the same represented items.
• Add an alternative interaction path such as keyboard navigation, zooming, or filtering when the visible mark cannot be enlarged.