Group by region

Claim: what belongs together is shown by a bounded region or a joining line, with colour as a second cue and never the only one.

• Grade: supported with caveat (laboratory evidence).
• Evidence: review, strand 2.
• Check: figure-judgment (judgment): is membership shown by colour alone anywhere?
• Reader styles: none changes it.

What it asks

• Draw a group as a box around its members, or join its members by a line.
• Colour follows colour as a signal: one colour per kind of thing, never the only cue.

Why

Items inside one bounded region are seen as a group, which can override proximity and similarity (Palmer 1992). Colour must never be the only cue (W3C 2023c).

Limits

• The evidence is from laboratory displays, not diagrams. Grouping by a joining line (Palmer and Rock, 1994) was not read.