The author spends the first 100 pages expaining why pictures are a good idea. He could have made his point much quicker and spent more time explaining his frameworks for drawing pictures, of which there are very many. He makes an analogy with a swiss army knife: his has 18 tools on it, culminating in a 6x5x2 = 60-picture grid of the different drawings you can make, which he calls the "visual thinking codex". The types of pictures he is talking about are: who/what, how much, where, when, how and why for the 6, and simple/elaborate, quality/quantity, vision/execution, individual/comparison and change/as-is for the 5x2.
On a side note, the book contains a "how to lie with statistics" error on pages 92-103, where he uses the area of an equilateral triangle to represent size. The area does not scale linearly with the sides, so a triangle that should be twice as large is now four times as large. He might have scaled the triangles to fit, but neither the sides nor the areas of the triangles scale with the numbers he's representing. Here's where I would keep it simple (and correct!) and go with bar charts.