A legend's entries should list in the same order the series appear in the chart itself

What it is

When a legend is unavoidable, its entry order must mirror the categories' spatial order in the graphic: the first legend item answers the foremost series (topmost or leftmost), the second item the second, and so on. With matched order, matching drops from "compare colours entry by entry" to "correspond by position" — one glance narrows the candidate; with scrambled order, every lookup is a full-table scan.

Why it happens

Matched order works by converting feature matching into position matching: the eye tracks sequence position far more reliably than it remembers colours, so when the graphic order and the legend order run parallel, readers can narrow candidates by "which line answers which item" and use the colour check only as final confirmation. Scramble the order and the shortcut disappears — colour becomes the sole cue and the working-memory burden returns in full. That is the entire justification for legend-order conventions.

Where it stops holding

"Graphic order" is chart-specific: line charts order by the vertical sequence of line endpoints, bars by bar arrangement, stacked charts by stacking order (note that some industry conventions reverse the legend so its first item answers the topmost layer — what matters is strict correspondence with the graphic's layer order, not the direction). Pie sectors have no linear order; there, order the legend by value or semantic grouping and keep it consistent across the product. Positional correspondence is a shortcut, not a hard law — cross-chart consistency is the baseline that outranks precision of correspondence.

Applying it

• Fix the categories' order of appearance in the graphic first, then copy that order into the legend verbatim — not by value, not alphabetically, not by aesthetics.
• For stacked charts, align the legend's first item with the top layer (or uniformly with the bottom) and keep the direction consistent product-wide.
• Verification: ask readers to locate the nth specified series; with matched order the first round-trip should lock on — repeated shuttling means the legend order has drifted from the graphic.

Related

• Same group: U5.01.1 Legends force eye round-trips between chart and key · U5.01.2 Direct labelling eliminates the round-trip
• Nearby: U5.02.2 Legend arrangement direction should match the graphic's spatial order · U5.04.2 Value sorting makes rank and extremes readable without search
• Search terms: legend order · position correspondence · stacked legend order