Choosing Line Graph Markers

Summary: Differences in color/shade are better than differences in shape. Graphs with more than 4 markers will need special treatment.

Details

The human brain is better at distinguishing differences in color or shade compared to differences in shape (The Functional Art, p. 110).

It is much easier to distinguish the two different lines in Example 2 compared with Example 1 below. It’s fine to also vary the shape of markers (Example 3).1

Two examples of line markers

Note that it becomes difficult for viewers to keep more than 4 or 5 colors straight (this is related to limits on visual working memory; see The Functional Art, p. 138). So if you have more than 4 lines on your graph, consider labeling the line directly rather than using a legend.

  1. Note that it can be difficult at first glance to notice the difference between Example 2 and 3. This underscores how much better our brains are at processing color differences compared to shape differences. ↩