[tz] Definition of "timezone"

[Paul Eggert]

On 2023-12-21 07:08, ApoY2k wrote:
> do you (or your
> peers on the tz project) consider a "timezone" to be inherently tied to the
> real-world geographical features they are used for, or is the word
> "timezone" in this context more broader understood as "any 'Zone' entry in
> the tzdb" - which would e.g. also denote "Etc/UTC" as a "real timezone".

I'll cc this to tz at iana.org to see what others think.

There's no formal definition.

In TZDB commentary I tend to use "timezone" roughly as a synonym for "TZ 
setting", that is, for valid values of the TZ environment variable. In 
that sense there is a huge number of timezones since this includes POSIX 
TZ strings, and "Europe/London", "Etc/UTC" and 
"GMT0BST,M3.5.0/1,M10.5.0" all denote timezones.

In contrast, the TZDB commentary uses "time zone" for the more common 
understanding in the real world, that is, the maximal-sized geographical 
region where clocks currently all have the same reading. In that sense 
there are 37 time zones right now, though the number changes depending 
on when you ask the question.

The TZDB commentary doesn't use a name for the concept you're asking 
about, but I suppose "geographical timezone" would do.

Admittedly the terminology is not always clear in this area.

PS. I got the number "37" as follows:

$ tzselect
Please identify a location so that time zone rules can be set correctly.
Please select a continent, ocean, "coord", "TZ", "time", or "now".
  1) Africa
  2) Americas
  3) Antarctica
  4) Arctic Ocean
  5) Asia
  6) Atlantic Ocean
  7) Australia
  8) Europe
  9) Indian Ocean
10) Pacific Ocean
11) coord - I want to use geographical coordinates.
12) TZ - I want to specify the timezone using the POSIX TZ format.
13) time - I know local time already.
14) now - Like "time", but configure only for timestamps from now on.
#? 14
The system says Universal Time is Thu Dec 21 20:00.
Assuming that's correct, what is the local time?
  1) Thu Dec 21 09:00  14) Thu Dec 21 20:00  27) Fri Dec 22 04:00
  2) Thu Dec 21 10:00  15) Thu Dec 21 21:00  28) Fri Dec 22 04:45
  3) Thu Dec 21 10:30  16) Thu Dec 21 22:00  29) Fri Dec 22 05:00
  4) Thu Dec 21 11:00  17) Thu Dec 21 23:00  30) Fri Dec 22 05:30
  5) Thu Dec 21 12:00  18) Thu Dec 21 23:30  31) Fri Dec 22 06:00
  6) Thu Dec 21 13:00  19) Fri Dec 22 00:00  32) Fri Dec 22 06:30
  7) Thu Dec 21 14:00  20) Fri Dec 22 00:30  33) Fri Dec 22 07:00
  8) Thu Dec 21 15:00  21) Fri Dec 22 01:00  34) Fri Dec 22 08:00
  9) Thu Dec 21 16:00  22) Fri Dec 22 01:30  35) Fri Dec 22 09:00
10) Thu Dec 21 16:30  23) Fri Dec 22 01:45  36) Fri Dec 22 09:45
11) Thu Dec 21 17:00  24) Fri Dec 22 02:00  37) Fri Dec 22 10:00
12) Thu Dec 21 18:00  25) Fri Dec 22 02:30
13) Thu Dec 21 19:00  26) Fri Dec 22 03:00
#?