Timelines

What it is

A timeline makes time visible. It can show a handful of milestones, a long historical sequence, phases of a project, or changes measured over a period. Its main promise is orientation: what happened first, what overlapped, how long something lasted, and where the evidence is uncertain.

Choose the form according to the question. A dated sequence is useful when order matters. A scaled timeline is needed when intervals and duration matter. A line chart may communicate measured change better than a row of decorative milestones. Do not let the familiar horizontal line decide the answer before the information has been examined.

Audit the chronology

List each event with its date, source, date precision, description, and relationship to the others. Mark approximate dates, disputed dates, missing intervals, and events that continued over a span. Decide whose history the timeline tells and which voices or places are absent. A crisp graphic can give an unjustified feeling of certainty to incomplete material.

Write the central question in plain language: Are readers comparing durations, following a process, or learning which events influenced one another? This helps decide whether to show exact spacing, group events into periods, use parallel tracks, or split a dense history into several focused views.

Choose the time model

Sequence or scale

In an unscaled sequence, equal visual spacing means only “next”. Say so through the design or label. In a scaled timeline, distance represents elapsed time, so dates and intervals must be plotted consistently. Compressing an uneventful decade may be reasonable in an editorial story, but the break must be visible and explained.

For irregular or missing measurements, show the gaps. The UK Office for National Statistics advises leaving gaps in a line chart where regular data is missing rather than implying continuity. The same honesty matters in timelines: a line that looks continuous can suggest knowledge the source does not provide.

Layers and relationships

Use lanes only when comparison is useful, such as parallel organisations, locations, or phases. Align events that share dates, distinguish a point event from a duration, and place explanatory notes close to the relevant moment. If arrows show influence or causality, verify that relationship; chronology alone does not prove cause.

Keep labels concise and let longer context live in captions or expandable detail. A timeline crowded with full paragraphs becomes difficult to scan. If the story needs substantial prose, a short annotated chronology beside an article may serve the reader better.

Design for real sizes

Prototype the timeline at the width where people will use it. On mobile, a long horizontal graphic can become a frustrating pan. Consider a vertical sequence that preserves the dates and relationships, or separate overview and detail views. If the timeline is interactive, make the same essential information available by keyboard and in a linear reading order.

Use text and shape as well as colour to distinguish tracks. Provide a concise text account of the main sequence and, for information-rich graphics, a fuller alternative description or table. The W3C guidance on complex images explains why a short image label alone cannot carry a detailed chart or chronology.

Review the interpretation

Ask a reader to identify the first event, the longest interval, an overlap, and a gap. Then ask what they believe caused a turning point. Compare those answers with the source material. If the graphic implies a stronger relationship than the evidence supports, adjust spacing, annotations, or wording.

Keep a source list and editable event table with the artwork. When a new date or correction arrives, the team should be able to update the sequence without rebuilding it from a flattened image. Giorgia Lupi’s Dear Data offers a useful reminder that the key and collection method are part of the story a data graphic tells.

Common mistake

Making every event equally spaced while allowing the reader to assume the line represents elapsed time. State the model clearly and preserve meaningful gaps, durations, and uncertainty.