Complex graphics need a long description
Aliases: longdesc · complex image · chart alternative
What it is
Flowcharts, statistical charts, and structural diagrams lay relationships out in two dimensions. A short alternative can name the graphic; it cannot finish those relationships. Graphics of this kind need a long description — a text channel roughly equivalent to seeing the figure. The short alt still belongs there, to identify what the figure is and that a longer equivalent exists. How to write the trend, whether it sits beside the figure or on a linked page, and whether a data table is required, are the next group’s craft. This leaf only gates the need: a short alt is not a substitute.
Why it happens
A short name rides the narrow accessible-name slot, built to announce controls and the identity of an illustration, not to replay a multi-series chart. When density does not match, AT users get a filename or “chart” while sighted users get trend, outlier, and comparison — equivalence already broken at the entrance. A second layer: if the need for a long description is never a requirement, late fill-in tends to describe appearance (colors, legend shapes), because the writer cannot see the data intent. Lock the need first; writing comes after.
Interactive charts (filters, brushing) cannot keep a short name in sync with every view. They still need an equivalent that does not depend on the current pointer. Whether that equivalent is visible prose or a table is not this leaf.
Studying it
Cover the figure, give only the short alt, and ask whether people can answer the question the figure was meant to answer (which series rose, who is highest). Then open the long description. Record failure under short alt only.
Independent variables: presence of a long description, graphic type (flow / statistical / schematic). Dependent variables: accuracy on the key questions, whether a fuller text channel is known to exist.
Do not pass on “alt is non-empty.” Samples should include dashboards and paper-like figures, not only icons.
Where it stops holding
Simple photos, icons, and logos do not need a long description; a short name is enough. Pure decoration should be hidden, not given an empty essay. CAPTCHAs and signature canvases are not “complex graphics”; they need a different kind of alternative, not a trend note. If the neighboring paragraph already states everything the figure adds, the short alt may only name it — repeating the paragraph is duplication, not a missing long description.
Applying it
- For any figure that encodes relationships, steps, or comparisons, list “needs a long description” as a requirement. Do not wait to fill alt after launch.
- Keep the short alt as identification (the figure’s title) and make the longer equivalent discoverable.
- Do not stuff a paragraph into
altand call it handled; when the slot is too small, open another channel. - Verify: cover the figure and listen to the short name. If that name cannot answer the figure’s question and no other text can, log a missing long description — log the gap first, then move to how and where to write it.