[tz] Dropping coordinates from zone1970.tab?

Aurelien Jarno aurelien at aurel32.net
Thu Sep 30 07:51:04 UTC 2021

On 2021-09-29 14:50, Paul Eggert via tz wrote:
> On 9/29/21 14:26, Aurelien Jarno via tz wrote:
> > If you consider a world map to select the timezone, with each timezone
> > represented by a circle from the coordinates in the zone1970.tab
> zone1970.tab has never been intended as a "nice" geographical interface in
> that sense. At the end of this email is a tzselect sample session (using
> 2021a, so more-recent changes are irrelevant) that uses nearest-neighbor
> from the South Pole, employing zone1970.tab's data. As you can see, tzselect
> prompts with ten nearest neighbors that are all incorrect because the
> correct answer is Pacific/Auckland, which is nearly 6,000 km away.
> Akthough I'm sure this way of using tzselect could be improved a bit, it's
> hardly worth the trouble as almost nobody uses it this way (the few people
> who use tzselect, typically don't take choice "10)" below). Instead of
> tzselect, most people use maps based on data that are proprietary (or cited
> in tz-link.html) and are outside tzdb's scope. These maps commonly depict
> some tall skinny timezones one of which could easily incorporate both
> Auckland and the South Pole (such a timezone need not be visually
> contiguous), and this is what I suggest for user-facing interfaces based on
> distances. Riyadh and Syowa can be handled similarly.

The point is not about choosing a timezone from a location, but rather
being able to show the cities linked to the timezones on a map so that
end users can pickup their timezone visually. While timezones concept
might sometimes be difficult to end users, they are usually aware if a
city near to their location "has the same time or not". I took the
example of Antarctica/Syowa and Asia/Riyadh as those locations are very
far, but with tzdata 2021b you can find other examples in the Carribean
region, for instance Nassau which is a link to Toronto.

The other alternative for end users to select a timezone, is to present
them with all timezones matching their country (using ISO 3166). This is
getting more and more difficult with timezone being merged in
zone1970.tab, you end-up showing timezones that look unrelated for end

Note that all the information for providing nice ways to select a
timezone for end-users is available in zone.tab, but that file is
currently deprecated in favor of zone1970.tab. I guess it will just get
removed when the process of merging timezone is finished. Undeprecating
it would solve all those issues.

Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien at aurel32.net                 http://www.aurel32.net

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