As Nightingale quipped when sending one of her analytical books to the Queen, “She may look at it because it has pictures.”[3] It’s a cynical, almost contemptuous, thing to write. But it is true. A chart has a special power. Our visual sense is potent, perhaps too potent. The word “see” is often used as a direct synonym for “understand”—“I see what you mean.” Yet sometimes we see but we don’t understand; worse, we see, then “understand” something that isn’t true at all. Done well, a picture of data is worth the proverbial thousand words. It is more than persuasive; it shows us things we could
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