A line chart connects points with lines to show numerical change. It is most often used for time series, with time or ordered sequence on the X-axis and quantity on the Y-axis. It makes trends, increases, decreases, cycles, and turning points easy to see.
Historical Background
Line charts date back to the late eighteenth century. William Playfair used line charts in The Commercial and Political Atlas in 1786 to show trade data over time. Since then, line charts have become one of the most universal forms in science, government, journalism, and business.
Data Structure
| Data | Role |
|---|---|
| Time or sequence | X-axis |
| Numeric value | Y-axis |
| Series | Optional multiple lines |
Purpose
The purpose is to show change over ordered values, especially time. Line charts are strongest when the continuity or trajectory between points matters.
Design Notes
- Use line charts for ordered or continuous X-values.
- Do not connect unrelated categories.
- Label axes and units clearly.
- Use direct labels when multiple lines are present.
- Avoid too many overlapping series.
Summary
Line charts are the standard chart for showing change over time. Their strength is continuity: they let readers see direction, slope, and pattern at a glance.
