Clive D.W. Feather <clive@davros.org> wrote on Tue, 20 Feb 2018 at 17:59:28 +0000 in <20180220175928.GB49012@davros.org>:
The correct answer is that if New York and Boston ever do different things, no matter what they are, then the existing America/New_York will be forked into two (or more) zones. New York will stay in that one.
That's a correct statement, but it's not an answer to the question of whether it's better to put a city in US/Eastern or America/New_York. It's certainly not a "correct answer" to the question asked. (It's also, kind of, obvious and was not what was being queried.)
Is there an official source for which parts of the US are *currently* in which time zones (including different summer time transitions)?
Sure. Although it's something like 57 different sources (combination of each state/territory's government plus the the US Code). Although tracking down the provenance accurately might be a lot of effort, we can generally assume that claims in the comments of "northamerica" are accurate.
If there is, then is there such a source for every date from 1970 onwards? If so, then that could be converted to form what you want.
Well, again, no, that's not my point. Let's presume the tz database has accurately captured the relevant transitions in the United States since 1970. As such, the relevant zones in "northamerica" and "australasia" are sufficient. This isn't about creating zones. It's just about mapping or tagging them. It also turns out that for my purposes, history was not terribly important.
Does someone (Paul?) want to convince me that it's Wrong to use the "backward" zones, for the narrow (but common) case of United States of America cities?
I'm not sure what the point of them is, so I can't comment.
For one thing, they reflect how the state and federal governments describe their zones. They are the common language both of the citizens on the ground and also legal instruments. --jhawk@mit.edu John Hawkinson