[tz] Comments and mapping of tz zones to the real world

Guy Harris guy at alum.mit.edu
Tue May 8 22:45:15 UTC 2012

On May 5, 2012, at 11:03 PM, Tobias Conradi wrote:

> Can you tell a way of how a user determines the correct zone for a
> random location in Indiana, selecting between
> America/Indiana/Indianapolis
> America/Indiana/Vincennes
> America/Indiana/Winamac
> America/Indiana/Marengo
> America/Indiana/Petersburg
> America/Indiana/Vevay
> America/Kentucky/Louisville
> America/New York
> without reading the comments?

Well, on the machine on which I'm typing this, they do so by launching System Preferences, clicking on "Date & Time", and either:

	1) checking the "Set time zone automatically using current location" check box and letting the computer do the work of figuring out where you are and what zone would be appropriate


	2) dragging the blue "current time zone" stripe to "Eastern Standard Time" if it's not already there, or clicking on the map near Indiana, and selecting the appropriate entry from the "Closest City" drop-down list.

I don't know whether any other desktop environments, or Linux distributions etc. that use those desktop environments, offer something similar to either of those (I tried it with Ubuntu 10.10 and it just offered a drop-down list of zone names and a map with cities to click on).

I.e., the *user*, in the sense of "the end user", shouldn't have to even know about the time zone names; there should be a layer of software doing a better job of letting the user select the zone (or selecting it for them).  The Theory file says:

> This naming convention is not intended for use by inexperienced users 
> to select TZ values by themselves (though they can of course examine
> and reuse existing settings).  Distributors should provide
> documentation and/or a simple selection interface that explains the
> names; see the 'tzselect' program supplied with this distribution for
> one example.

However, that then means that the authors of the software, and the maintainers of whatever databases it uses, would need to figure out the right zones for particular locations, and the comments might help there.

The comments aren't "part of the database" in the sense that zic reads them and produces a file based on what they say.  They could, however, perhaps be viewed as "part of the database" in the sense that they are documentation for the database, in which case an error in a comment would be a documentation bug for the database.

Some might argue that the database should include additional information, in machine-readable form, to, for example, give a "closest city", or some other regular-user-friendly descriptive information, for each zone, for use by that software.  Unless the tz database takes on the burden of localization, however, that information would have to be in some form that would allow lookup in a database of localized names for cities.  Currently, the Unicode Common Locale Data Repository:


has localized exemplarCity names for tz database zones:


I don't know whether the maintainers of the CLDR use the tz database comments to pick the exemplarCity values.

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