Yau provides a comprehensive introduction to data visualisation: why you want to do it, what kinds of approaches are available, and how to use them in detail.
Given how much Yau emphasises the need to make the area (rather than the radius) of a circular blob proportional to the data quantity it represents, to avoid visual bias, I am surprised that he doesn’t give similar clear warnings about choropleth maps (those where each country, or other region, is coloured to represent the data for that region). Different countries have different sizes, which can again bias the visual effect.
Apart from this one minor caveat, this is an excellent introduction to visualisation. The reader can hit the ground running, and produce beautiful chartjunk-free charts that tell the story of the data clearly, without misrepresenting it.