Time Series Data

Time series visualizations track the evolution of one or more variables over a period of time. The X-axis is strictly reserved for time, progressing from left to right.

Line Charts

The standard for continuous data. Connecting points with a line implies continuity between those points.

Rule	Why
Direct Labeling	Place the label (e.g., "Revenue") directly at the end of the line on the right side. Avoid separate legends which force the user's eyes to bounce back and forth.
Bank to 45 Degrees	Adjust the aspect ratio of the chart so the average slope of the lines is roughly 45 degrees. This maximizes our ability to perceive changes in slope.

Area Charts

A line chart where the area below the line is filled. It emphasizes the volume or magnitude of the data rather than just the trend.

Warning: Stacked Area Charts are notoriously difficult to read. The top band's shape is heavily influenced by the fluctuations of the bands beneath it, not just its own data.

Common Mistakes

• Uneven intervals: If your data points are Jan, Feb, Mar, Dec, they cannot be evenly spaced on the X-axis. The physical distance on the screen must match the temporal distance in reality.
• Spaghetti Charts: Plotting 10 different lines on the same axis creates an illegible tangle. Use small multiples (a grid of 10 small charts, one for each line, sharing the same scale) instead.

Next Steps

Calculate the perfect container size for your time series using the Aspect Ratio Tool.