The EU published a chart showing the scale of trading relationships with various partners. It uses circles to represent amounts, and I've blogged about this before (well, it's nine years ago now...).
You shouldn't do that because humans can't compare volumes as well as they compare lengths. This is what Isotype was about...
Below left is the comparison they made. Then I've show the comparison by length, and, even better, horizontal bars with a block for every 10 billion and the figures provided.
According to Politico.eu:
'David Spiegelhalter, a professor of the public understanding of risk at Cambridge University, said the Commission's approach was "indefensible" and went against "standard graphical practice."
"It's also the biggest mistake to make. It's incorrect to use diameter to represent volume," he said, adding that it was "the sort of thing a junior person would do."'...or a graphic designer, I'm afraid.