I think Chapters 4, 5, 6 are some general introduction to visualization. Although at this stage, I haven’t completed Chapter 6 and onward, I think the chapters are to prepare readers for more advanced topics and the author put those chapters in for completeness.
The summary of Chapter 5 is actually simple: less is more. The objective of using graphs to communicate numerical information is to make it easy for your readers to understand the information. If the graph is not easier to understand than the table of numbers, then the graph is a failure. Sometimes, we like to decorate our graphs, adding 3D visuals for example. However, decoration is not analysis.
I think it is all about communication. We want to communicate our findings and analysis effectively to our audience and hopefully, we can persuade them to take action. We are not doing fancy visualization to show off our chart plotting skills or software skills.
Finally, the author seems really don’t like the Radar Plot. He said, “Radar plots are pure obfuscation, and should not be used under any circumstance.” I do not fully agree that it is the issue of the radar plot. For example, a radar plot is quite useful in showing the dominant wind direction in a region. But I agree that plots/charts should be simple and made communication easier.