[tz] time zones only ?

Guy Harris gharris at sonic.net
Thu Feb 25 23:42:24 UTC 2021

On Feb 25, 2021, at 3:18 PM, William Karlsson via tz <tz at iana.org> wrote:

> Is there a simple way to compile only the timezones ? i.e. US/Central etc... No cities ?


The best way to think of the database, the "z" in "tzdb" and "tz at iana.org" and the "zone" in "time zone database" notwithstanding, is as a database of *regions*, not "time zones".

For one thing, a time zone, in the usual sense, can include locations that don't follow the same daylight saving time rules; for example, the Mountain Time Zone in the US includes  Arizona, which (outside of the Navajo Nation) doesn't follow DST, as well as several states that do.

In addition, a given location can move from one time zone to another.

Even when the pre-city names were the primary names in the tzdb, the database didn't have "only the timezones".  It had a region named "US/Mountain", but it also had a region named "US/Arizona", for the reason mentioned above, along with US/East-Indiana and US/Indiana-Starke.

To quote the theory.html file:

Each timezone typically corresponds to a geographical region that is smaller than a traditional time zone, because clocks in a timezone all agree after 1970 whereas a traditional time zone merely specifies current standard time. For example, applications that deal with current and future timestamps in the traditional North American mountain time zone can choose from the timezones America/Denver which observes US-style daylight saving time, America/Mazatlan which observes Mexican-style DST, and America/Phoenix which does not observe DST. Applications that also deal with past timestamps in the mountain time zone can choose from over a dozen timezones, such as America/Boise, America/Edmonton, andAmerica/Hermosillo, each of which currently uses mountain time but differs from other timezones for some timestamps after 1970.

The city names were chosen a while ago as the way to identify regions.

The source files for the database have entries for regions ("timezones"), not for "traditional time zones"; it produces files for all the regions, and then constructs backward compatibility links, using the old names, from the "backward" file.

What are you trying to accomplish here? 

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