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 (https://doi.org/10.1145/238386.238400">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.