Figures: how to draw a figure or a diagram for a reader

Question: how should a figure or a diagram be drawn, in any document of the family, so that a reader understands its message quickly and correctly, can reach it without sight, and trusts it.

Scope: any drawn picture in a document: a chart, a node-link diagram, a schematic (decision 0006). Colour and motion on slides stay in the presentations topic (strands 7 and 8). The theory of diagram notations and the layout studies of software diagrams are in reader-ergonomics-software-design's system diagrams review, linked, not reviewed again.

Steps: frame · protocol · sources · review · state of the art · position · against · baseline · bibliography

Claims

Claim	Grade	Where
Of five layout aesthetics, fewer edge crossings had the largest effect on understanding a node-link diagram	measured	review.md 1
Crossings that remain cost least near 90 degrees	supported with caveat (small samples)	review.md 1
One study found layouts with crossings fastest to interpret, while readers preferred none	supported with caveat (26 participants)	review.md 1, against.md
For quantities, position on a common scale is read more accurately than length, angle or area	measured, for charts	review.md 2
Items inside one bounded region are seen as a group, which can override proximity	measured, in the laboratory	review.md 2
Beauty gives a small gain in performance: g = 0.12 over 25 studies, g = 0.29 over 31	measured, for interfaces	review.md 3
Embellished charts were described as accurately as plain ones and remembered better weeks later; other embellishments slowed search or lowered accuracy	measured, disputed	review.md 3, against.md
Text art is non-text content: it needs a text alternative like any image	convention (a standard)	review.md 4
A complex diagram needs a short and a long text alternative; a filename is a failure	convention (a standard)	review.md 4
Lines and fills that carry meaning need 3:1 contrast against what lies next to them	convention (a standard)	review.md 4
No study tests text art against a drawn diagram, with readers or with screen-reader users	not found	review.md 4
Style guides agree on a stated message, direct labels and little decoration, without studies behind them	convention, untested	review.md 5