[tz] Add new timezone for Hanoi Capital, Vietnam

[Tim Parenti]

On Mon, 18 Feb 2019 at 11:37, KP <khaiphan9x at gmail.com> wrote:

> Countries including Cambodia, Laos and South Vietnam (regardless of
> agreement) have their own time zones, except North Vietnam. Is it an
> omission or bias?
>

Not really.  Cambodia and Laos are linked to Asia/Bangkok as well:

# Thailand
# Zone  NAME            GMTOFF  RULES   FORMAT  [UNTIL]
Zone    Asia/Bangkok    6:42:04 -       LMT     1880
                        6:42:04 -       BMT     1920 Apr # Bangkok Mean Time
                        7:00    -       +07
Link Asia/Bangkok Asia/Phnom_Penh       # Cambodia
Link Asia/Bangkok Asia/Vientiane        # Laos

That said, it does look like Asia/Hanoi (which currently exists in the
backzone file) should indeed be linked here as well for the same reasons,
since Asia/Ho_Chi_Minh does differ from these from 1970 to 1975.  It would
appear that was an oversight due to the various complexities.

Commentary should also be added in the Vietnam section of the file, if the
link isn't added there.  Or perhaps this is indeed a complex enough case to
warrant bringing Asia/Hanoi out of backzone.  Either way, the name should
be in the main distribution somewhere, since Asia/Ho_Chi_Minh is not
representative of Vietnam alone.

On Mon, 18 Feb 2019 at 10:13, Clive D.W. Feather <clive at davros.org> wrote:

> Hmm, do we need another zone for that? Or will there be a string of such
> zones as the border moved south? I don't know the history of Vietnam well
> enough to know.


I should hope that in post-1970 cases of incremental territorial shifts, we
can treat this a bit like we treat Asia/Urumqi: The geographical boundaries
are/were fluid/undefined, and you simply choose the file that adheres to
whichever timescale is most appropriate for your situation.  The line
between limiting ourselves to the two "major" zones and creating a new zone
for each city as it was captured may be fuzzy, but I'm pretty confident
that line exists somewhere in there.

--
Tim Parenti

>
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