Which column a table is sorted by, and in which direction, needs to stay visible at all times

What it is

Sorting is one of the chart's implicit coordinate systems, and its basis (which column, ascending or descending) must be visible at all times: the header's sort arrow, the toolbar's sort state, or a caption statement. On a chart whose sort basis is invisible, readers cannot tell "by what right the top items sit on top" — none of the information carried by order can be decoded correctly, and it can even be decoded backwards.

Why it happens

Invisible basis causes attribution errors: readers seeing descending order assume "sorted by the primary metric," and when the actual basis is date or another column, they read positional relations as magnitude relations that do not exist. This is most dangerous in multi-column interactive tables — after three sort clicks, the current state lives only in the memory of the last click, and in a screenshot, a share, or a next-day revisit the order has no provenance. Visible sort state also supports collaboration: "sorted by conversion rate, descending" is a checkable claim only when the state is visible. Static charts (caption statements) and interactive views (header indicators) are two forms of the same requirement.

Where it stops holding

Visibility comes in tiers: single-column sorting needs only the header arrow; multi-level sorting (by department, then by value) needs an explicit sort-state bar listing every level. Sort state must also enjoy parity with data state — visible filters with invisible sort is a common half-finished job. Sharing and export are the stress tests: an exported image or printout without sort indication leaves receivers with no way to interpret the order, so export templates should embed the sort statement.

Applying it

• Keep a persistent sort-direction indicator in table headers, with a sort-state bar for multi-level sorting.
• Attach the sort statement to exports and screenshots by default (watermark zone or caption line).
• Verification: send a screenshot of a sorted table to an uninvolved colleague and ask "what is this sorted by?"; a wrong answer means the indication is insufficient — add the state display.

Related

• Same group: U6.08.1 Sorting is the cheapest device for discovering structure · U6.08.2 The default sort shapes the overwhelming majority of readings
• Nearby: U5.04.5 State the sorting basis in the axis title or caption · U6.03.1 Applied filters must all be visible
• Search terms: sort indicator · sort state visibility · table header sorting