The essay examines the guideline of the "principle of proportional ink" (closely tied to misleading axes) and defined as “when a shaded region is used to represent a numerical value, the area of that shaded region should be directly proportional to the corresponding value.” This idea was derived in Edward Tufte’s book The Visual Display of Quantitative Information (1983, p.56).
The article defends the guidelines mentioned in the “Misleading axes on graphs” essay where it was emphasized that bar charts must start at zero on the vertical-axes; however, line charts are not required to do so.
The article first examines bar charts with respect to the principal of proportional ink. They reference a misleading graph of the top most read books---which misleads viewers into not realizing that some volumes had higher sales (e.g. Anne Frank vs. The Da Vinci Code). (On a side-note, the graphs does not even explain how the data was collected for the graph.)
The article then examines line charts with respect to the principal of proportional ink. They emphasize that line charts do not use shaded volumes to indicate quantities so therefore they are not required to start at zero. This point leads to a discussion about shaded line-charts---which should therefore have a scale that goes to zero.
The article then examines bubble charts with respect to the principal of proportional ink. The authors take the position that, “the power of the bubble chart is that by using color and size as well as vertical and horizontal position, one can simultaneously encode four different attributes for each item in the dataset.” The authors references a visualization by Hans Rosling.
The article then examines donut bar charts with respect to the principal of proportional ink. The authors express that, “the problem with this type of visualization is that the geometry of the circle assigns a disproportionate amount of ink to bars further on the outside.”
The authors then discuss topics where the a changing denominator can effect the guideline of proportional ink. As far as three dimensional graphs go, the authors note that they should have more than one independent variable and that the use of perspective makes the relative size of the chart elements hard to interpret.
Finally, the authors review pie charts. One point they note highlight is that, “the main problem with 3D pie charts that in these graphics, the front-most wedges of the pie chart to appear to be larger than the rear wedges.” Therefore, this breaks their proportional ink guideline.
I really liked reading the critiques in the article. One good point to review here is that graphs in the authors’ opinions are to improve the data messages conveyed to viewers. I will suggest that the questions be put to a vote or included into a study? I am curious to learn if it would be an interesting study measuring view beliefs from the different representations and wonder what the class thinks.