Cities:
Reader Michael Lorton poses this puzzle: What do Naples (Italy), Novgorod (Russia), and Chiang Mai (Thailand) have in common?
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Cities:
Reader Michael Lorton poses this puzzle: What do Naples (Italy), Novgorod (Russia), and Chiang Mai (Thailand) have in common? 
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Kota Bharu, Malaysia
What, you don't like Neapolitan iced cream?
There's more. See this similar question at Language Hat about 14 months ago.
"Delenda est"
That said, the fact that all three cities can be (or as originally named, could have been) called "New City" in English does seem to be the most interesting (though certainly not the most important) shared feature. But what possible criteria can be used to determine what feature is most interesting?
For example, if you chose 3 cities at random from around the world, you have a very high chance of getting 3 all in the Northern hemisphere, all not containing Daniel Chapman's kitchen, and a 100% chance that they are not inhabited by 8foot tall people. Thus, those are all clearly not the right answer.
Mr. Spock, BTW, knew this, and he generally was quite good at giving Captain Kirk the most pertinent answer.
Thanks, Derek, for Kota Bharu and Villanova (although less sincerely for the latter, because I am just so annoyed at myself for not coming up with it first). I left out Newton on purpose  it makes the puzzle too easy.
Michael
Cartagena, Spain is Cathago Nova; i.e. New New City.
DK's "unstated rule of statistical significance" and Volokh's fauning reply ("cool") are obviously incorrect.
According to DK, "pattern" answers seeking a property from a subset X of a larger set Y actually seek a property of X not likely to be shared by a randomly selected subset of Y.
But this notion is absurd. Suppose I ask "what property is shared by the numbers 11, 17, 29, and 71"? The correct answer is that these are each primes two smaller than a twin prime. But by DK's proposed rule, the correct answer is something like "they are each roots of the polynomial (x11)(x17)(x29)(x71)."
To really understand what is happening, one must understand learning theory and to some extent Kolmogorov complexity: we are seeking concise and plausible short descriptions that best explain a set of observations. See, e.g. http://www.idsia.ch/~marcus/kolmo.htm .
If you come up with something that describes the three things, and only the three things, amongst all things in the world (not related to the fact that they were chosen itself), then haven't you won the game?
It's equally painful watching mathematicians struggle with spelling. Although he is doubtless a dear, I don't think Eugene was "fauning."
Apologies for the cervine misspelling; I hope it "does" not cause a "row."