Preparing plots for publication

In this blog post I will discuss some tips my advisor at Stanford taught me at the beginning of my Ph.D. We will discuss how to use Edward Tufte's principle of maximizing the ratio of information to ink to prepare plots for publication.

The first step is to identify elements in the plot that are not contributing to the information being presented. In a typical plot generated by scientific softwares such as the one shown in Figure 1, the right and top lines of the bounding box do not provide any information. Also, if the plot's purpose is to show the general trend, as is the case with most statistical plots, the grid lines add little information. Thus, to maximize the information to ink ratio we remove the top and the right lines of the bounding box, and the gray grid lines.

Figure 1. Plot generated by the software.

The plot after the removal of lines from the bounding box and the grid lines is shown in Figure 2. We now need to assess the ratio of the information added by the tick marks to the number of pixels they occupy. Too many tick marks generally crowd the axis without adding much information. In the example plot I decided to half the number of tick marks on x-axis, and use only 4 tick marks on the y-axis. Choosing the appropriate number of axis ticks is a subjective decision and I generally experiment with different combinations.

Figure 2. Plot after removing grid lines and the bounding box.

Figure 3 shows the modified plot after reducing the axis ticks. At this stage, removing any element from the plot will result in a loss of information. One can argue that the axis lines are not adding much information either, so they can be made thinner or even be removed. I generally do not recommend removing or reducing the weight of the axis line for print publications, as the departure from convention can throw some readers off. However, this can be tried in presentations when the presenter will actively guide the listener through the plot.

Figure 3. Plot after reducing the number of tick marks.

Once I determine that all elements present on the plot are adding information, I increase their visual weight to enhance readability. Since everything in the figure is now adding information, adding ink or pixels to enhance weight does not change the information to ink ratio. The final plot after increasing the visual weight of the elements is shown in Figure 4.

Figure 4. Final figure ready for publication.

The process described above is summarized by the animation in Figure 5.

Figure 5. Summary of the steps taken to prepare the illustration for publication.

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