Graphical relationships representing comparisons of categorical variables aren’t very common. They are conceptually not very difficult, but few tools have provided a ready way to generate suitable figures (scatter plots, bar charts, and pie charts are more readily found). However, tools like GGally in R make complex graphs accessible, and that package provides a figure style that is a grid of rectangles with proportional areas.
In Figure 1, the proporition of Titanic survivors by sex is shown, where larger rectangles indicate a larger absolute count (here, area is proportional to count).
Note
This representation is an intuitive graphical version of the comparisons in a chi-square test.
One advantage of this representation is that we can use the stacked bar representation (see above) to subdivide each of the rectangular areas by a further categorical variable, as in Figure 2 where we divide the blocks representing passengers conditioned on sex and survival, according to class.
