Like every year, the organization of the Malofiej World Infographics summit, workshops, and awards, has put together a beautiful book, the 23rd in the series (see the previous ones.) I wrote* a short chapter, titled 'Unknown Unknowns', which you can download as a PDF here. Scott Klein wrote another describing some old news graphics about cholera outbreaks, and ProPublica has just published it. It's a fantastic read, so do yourself a favor and take a look at it.
NOTE: You will find at least one typo in my article: Instead of “casual relationship” it should read “causal” (h/t Cristina Versino)
(*Better said, I adapted a couple of pages from The Truthful Art and then wrote a short introduction and a conclusion.)