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A few months ago I started using the Ultimate Geography Anki deck after performing quite abysmally on some silly geography quiz that was doing the rounds on Facebook. I now know where all the damn countries are, like an informed citizen of the world. This has proven itself very useful in a variety of ways, not least of which is in reading other material with a geographical backdrop. For example, the chapter in Guns, Germs and Steel on Africa is much more readable if you know where all the African countries are in relation to one another.
(In the process of doing this, coupled with an international event in Sweden, I've learned that the Scandinavian education systems are much, much better than that of the UK at teaching children about the rest of the world)
The geography deck was particularly easy to slip into because it developed an area I already (weakly) knew about. I'm looking for some new Anki content of a similar nature: a cross-domain-application body of knowledge I probably sort-of know a little bit already, that I can comprehensively improve upon.
Suggestions and anecdotes of similar experiences welcome.
KnaveOfAllTrades's idea of learning demographic & economic (GDP and its component parts) statistics of various places has occurred to me as a candidate for a useful Anki deck, so I second that.
Knowing some mathematical constants to a few significant figures can be useful. Memorizing √10 = 3.16 lets you interpret midpoints between ticks on a logarithmic scale, and √2 & √3 are the lengths of diagonals of unit squares & cubes. And knowing all three roots makes it easier to guesstimate square roots in general, using the √(ab) = (√a)(√b) result for ... (read more)