On Mon, 3 Nov 2025 at 13:48, Paul Eggert via tz <tz@iana.org> 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