This post is motivated by a comment on my blog post Line Charts Are Not Always the Best Way to Show Time Series. The comment by Meic Goodyear said, “A small point, but you could improve your Figure 2 chart by aligning the label on the vertical axis horizontally to make it more legible.” Here I will state my position on the placement of labels on the vertical axis.
Figure 1 shows four possible positions for the label on the Y-axis (the vertical axis.) I consider the top two to be acceptable and the bottom two to be unacceptable. I find the label on the bottom left the most difficult to read. Although the label on the bottom right is easy to read, it takes up too much valuable real estate. The most important elements of graphs are the data so we want to give as much space as possible to the data. I’ve seen longer labels positioned this way that called much too much attention to the label rather than the data. Notice that in this case making the vertical axis horizontal caused the Excel default for the horizontal labels to slant which I find distracting.
We are now left with the two positions on the top. Each has advantages and disadvantages. The placement on the left figure more clearly associates the label with the axis while the placement on the right is easier to read. I have no trouble reading the label on the left. Since this is often the default of software packages, I usually just leave this default and change options that I think make more of a difference. However, I recognize the advantages of the top right. It’s six of one and half dozen of the other.
As James Marcus and Hrvoje Smolic pointed out in the comments, the figures above might not be the best graphs for the situation. These figures address the GB used on a daily basis; a cumulative chart showing the GB remaining might be of more interest. While I certainly agree with their comments, they do not affect the placement of the axis label.
Please comment on the article here: Effective Graphs