On Mon, 3 Nov 2025 at 13:48, Paul Eggert via tz <[email protected]> wrote:
> Although this won't be "perfect" it should be good enough (and opinions
> will differ about what is "perfect").
…and that gets into an understated subtlety that I see folks
often forgetting about when attempting to balance the laudable goal of
simplifying UX against the true complexities of civil timekeeping. Of
course, most people and end-users only think about "time zones" in a
colloquial sense, if at all — ranging from coarse definitions ("where does
the time match now?") to some that are reasonably finer ("where does the
time match now and into the future?").
But everyday applications generally do ultimately need to store and display
*some* information about the past in addition to information about the
present and future. As such, any algorithmic simplification of the full
zone set will inevitably fail someone or something for *some purpose*,
because how you decide what to include and what to shed will vary.
(Indeed, extrapolating this — our 1970 cutoff surely frustrates many, but
is a long-standing compromise borne out of practicality.)
As an illustrative, but extreme and contrived example — If an entire
continent were to suddenly agree to unify all of its timezones tomorrow, I
would imagine that a great deal of folks would absolutely insist that their
apps still need to care about at least the recent history of timekeeping
throughout that area. It would be fairly reasonable for developers to want
their apps to retain and properly reference that recent historical data for
quite some time to come — for some, perhaps even for a duration
approximating "forever".
More realistically and more nuanced — Kazakhstan's two "time zones" (in the
colloquial sense) were merged about 20 months ago. Does your application
still need to care about the deeper timekeeping history there? Maybe! If
so, should you keep it around for another year? Five? Twenty? I don't
know! And no algorithm, however well-designed, will ever *truly* be able
to decide these things for you unless you can provide it with additional
information about your specific priorities. I'd imagine a developer of
apps where Kazakhstan is a key demographic would be likely to answer very
differently than someone whose sole focus is on, say, South America.
--
Tim Parenti
