I looked at CGP Grey’s Europe diagram yesterday and saw that it was outdated. Latvia and Lithuania are now in the Eurozone, and not just in the EU. I started with a blank sheet and worked my way through.
I also added the four countries that use the euro but aren’t in the EU: Andorra, Monaco, San Marino, and the Vatican. I did not add Montenegro and Kosovo to this zone: if I added them, I’d have to add Zimbabwe, as they all use the euro but aren’t approved by the Council to do so.
My diagram is rather simple, as it only shows what is useful to a person travelling or working in Europe. Nothing extraordinary like this one from Wikipedia: