Use line charts to convey continuous trend

Choose a line chart when the main job is to show continuous change across an ordered sequence. For example, connect the observations with a line for trend displays and avoid bars when you want readers to read rise, fall, and shape rather than separate amounts.

A connected line changes what readers think the data is about. The same vertical positions can be read as separate quantities in bars or as a continuous trajectory in a line, so the chart family itself guides interpretation.

Mechanism: Connecting points creates an affordance for continuity and trend, while bars emphasize individual comparisons between discrete values.

Evidence: The paper summarizes evidence that people describe the same values differently in bars and lines: bars elicit discrete comparisons, while lines elicit trend descriptions. It uses this result to argue that chart choice should follow the intended interpretation, not only position precision (Bertini et al., 2020).

• User Goal: Explain change, direction, or overall shape across a sequence.
• Task: Trend reading rather than point-by-point comparison.
• Data: Sequential observations with a meaningful order and an implied continuity.
• Chart Setting: You are choosing between a bar chart and a line chart for the same values.
• Audience: Readers who need the chart to cue a trend interpretation.
• Success Criterion: Readers describe the series in terms of rise, fall, slope, or overall shape.

Break it when: The main job is to compare separate values as independent observations. Why: The line introduces a continuity cue that can shift attention away from discrete comparisons.

Sacrifice: You give up some emphasis on separate item-by-item comparison. Risk: Readers may infer continuity where the data should be treated as distinct observations. Mitigation: Switch to bars when the message is comparison between separate values rather than trend.

Mistake: Adding a connecting line when the values should be read as separate comparisons. Why it fails: The connection itself suggests continuity and trend.

Failure Sign: Reviewers talk about individual amounts instead of the overall trajectory. Quick Check: Render the same data as both bars and a line, then ask a reviewer for a one-sentence description. Stronger Test: Keep the version that makes reviewers describe the intended trend without prompting.

• Replace bars with a connected line across the ordered observations.
• Keep the ordered sequence visible so the line reads as one trajectory.
• Remove the line and switch to bars if reviewers keep treating the sequence as separate comparisons.