Use a line graph to show general trends
For overview trend reading, prefer a line chart on quantitative point sequences to improve insight and mitigate point-by-point detail emphasis for viewers who need the gist.
- purpose:select
- basis:empirical
- task:trend
- chart:line:use
- chart:bar:avoid
- reading-mode:overview
- lever:chart-family
- quality:insight
advice
Choose the connected trend form
Choose a line graph when the chart’s job is to show the overall pattern quickly. For example, use a simple line graph instead of a bar graph when viewers need the gist or need to pick out the trend at a glance.
reason
Why connected marks fit trend reading
A connected trajectory frames the data as one changing pattern rather than as a set of separate vertical values.
Mechanism: Connecting adjacent points helps viewers read the display as a trend, which matches situations where the main goal is quick gist and extrapolation.
Evidence: Across the paper’s preference studies, participants chose line graphs more often for gist and trend scenarios, while bar graphs showed the opposite pattern for detail scenarios (Levy et al., 1996).
context
Use when the chart must communicate the overall pattern
- User Goal: Show the gist of the data.
- Task: Let viewers see the general trend quickly or extrapolate from it.
- Data: A sequence of quantitative points shown in order.
- Chart Setting: You are choosing between a line graph and a bar graph for a static display.
- Audience: Viewers who need the pattern quickly.
- Success Criterion: Viewers can state the overall trend after a brief glance.
exceptions
Do not use when point-by-point specifics are the priority
Break it when: The chart must show detailed relationships among individual data points. Why: In that situation, bar graphs were preferred over line graphs.
costs
Costs of emphasizing trend over detail
Sacrifice: Some emphasis on each individual value. Risk: A line graph can underplay the need to inspect specific point-to-point relationships. Mitigation: Switch to a bar graph if detailed inspection becomes the main task.
mistakes
Common misuse of the line choice
Mistake: Keeping a line graph when viewers are expected to answer detailed questions about individual points. Why it fails: The connected form supports gist better than point-by-point inspection.
check
Check the trend-vs-detail fit
Failure Sign: Reviewers focus on individual values instead of describing the overall pattern. Quick Check: Compare line and bar versions of the same data and ask which one better conveys the gist after a glance. Stronger Test: Show both versions briefly and ask viewers to describe the trend without discussing individual points first.
fix
Fix the chart family choice
- Replace separate vertical bars with one connected line through the same points.
- Redraw the graphic as a simple line graph if the current bar form is being used to show gist.
- Recheck the revised chart by asking viewers to summarize the trend at a glance.