Facet order should carry information, not alphabetical habit

What it is

The panel order of a facet array is the last and most squandered encoding channel. Defaults — alphabetical or data order — have nothing to do with any business structure, and readers scanning the array take away no order information. Make the order carry information: sort panels descending by each group's key quantity (total, growth, peak) and anomalies float to the ends; keep ordered dimensions (age bands, grades) in natural order and gradients read off at once; lay time facets in time order and the evolution unfolds. Ordered well, the array arrives with its conclusion; ordered badly, the conclusion is buried in a shuffle.

Why it happens

Scanning an array, readers advance by row-column order by default, and panels seen first gain higher attention and memory weight. Value ordering puts "important and anomalous" at the head of the scan path, effectively pre-screening visually; natural and time orders make between-panel differences correspond to an expected direction (later to the right, older downward), so readers detect anomalies through the mismatch between trend expectation and what they see. Alphabetical order abandons the channel entirely while still looking "orderly" — concealing the structure ordering could have carried.

Where it stops holding

Three legitimate orders: value order (by summary statistic), natural order (intrinsic order of ordinal dimensions), business order (fixed structures like regional or channel groupings). With two-level facets (rows and columns), give the primary dimension the rows and the secondary the columns, each following the rules above. Interactive settings offer order switches (value / natural / alphabetical) at near-zero cost; static reports should at least be able to justify alphabetical order — most of the time they cannot.

Applying it

• Default the facet template to key-value descending or natural order; alphabetical must be an explicit choice with a reason.
• For two-level facets, fix the row dimension (primary comparison) first, then the column dimension, each ordered by the rules above.
• Verification: after a three-second scan, readers should name "which panels matter most"; failure means the ordering carries no information.

Related

• Same group: U2.15.1 Small multiples replace overlay with repeated like-for-like panels · U2.15.2 All facets must share the same scale to be comparable · U2.15.4 Too many facets shrink panels below readability · U2.15.5 Small multiples compare shapes, not precise values
• Nearby: U2.02.3 Order categories by value, not alphabet · U2.10.2 Row and column ordering decides whether structure is visible
• Search terms: facet ordering · panel order · small multiples · ranking