http://www.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/deeplinks/2010/01/primer-information-theory-and-privacy
As of 2007, there were 21,733 people living in the 90210 area, only 452 in 40203, and around 6.625 billion on the planet.
Knowing my ZIP code is 90210: ΔS = - log2 (21,733/6,625,000,000) = 18.21 bits Knowing my ZIP code is 40203: ΔS = - log2 (452/6,625,000,000) = 23.81 bits Knowing that I live in Moscow: ΔS = -log2 (10524400/6,625,000,000) = 9.30 bits
How much entropy is needed to identify someone?