[tz] Add new timezone for Hanoi Capital, Vietnam

Hans-Joerg Happel happel at audriga.com
Mon Feb 18 19:43:35 UTC 2019

Dear KP,

to summarize and perhaps resolve some confusion, I see two points here:

>I would like to suggest adding a timezone for Hanoi or changing the name
>from Asia/Ho_Chi_Minh to Asia/Hanoi as the official timezone for Vietnam.

1) tzdb does not aim to provide or define a list of the current
"official timezone" for any country.

In contrast, it provides a list of official (and sometimes even
inofficial?) time zones which have been valid for some certain area of
the world from 1970 till now. Vietnam (VN) overlaps with two such areas
(via zone1970.tab as Tim pointed out): one labeled "Asia/Ho_Chi_Minh"
and one labeled "Asia/Bangkok", the latter covering a larger part of
Indochina including Hanoi.

Forming one single "official timezone" for Vietnam (or renaming
"Asia/Ho_Chi_Minh" to "Asia/Hanoi") would not be correct, as from the
1970-based perspective of tzdb, the Ho Chi Minh area (South VN) and the
Hanoi area (North VN) had different time zone rules (until 1975, as
pointed out).

So any system using tzdb data will require the implementer (or end user)
to choose if either "Asia/Ho_Chi_Minh" or "Asia/Bangkok" should be used
for any particular entered data, as it can make a difference for certain
calculations, due to different time zone rules in the past.

The special case here is that there are no more differences between
South + North VN time zones since 1975. In contrast to countries with
multiple time zones that are still differing today (e.g., Australia,
Russia or the US), one can thus argue that a distinction between South +
North VN time may not be practically relevant for many implementations,
as it would only make a difference for data between 1970-1975.

Any system implementer is free in offering end users a single "Vietnam
time", which e.g., internally maps to tzdb's "Asia/Ho_Chi_Minh".
However, this is up to any implementer and not to tzdb.

2) tzdb time zone names should rather be considered as (technical)
identifiers. So "Asia/Bangkok" (and its links such as "Asia/Phnom_Penh")
refer to the same set of time zone rules shared by that area.

This is not imply any Thai influence or "leadership" regarding this time
zone, but is a mere convention. If the Cambodian or Vietnamese
government would deviate their time zone rules anytime soon, tzdb would
automatically create separate identifiers - but only for "technical",
not for political reasons!

So tzdb's time zone "names" should not be taken too literal, as they do
not intend to be used as user-facing labels. Software implementers can
still apply localization and aliases on top of those identifiers.

It's part of the truth though, that tzdb names might surface to end
users at certain points. It's however not necessarily tzdb to blame for

(Both points based on my current understand of the state of affairs -
please feel free to correct me if I am wrong in some point)


On 18.02.19 11:21, KP wrote:
> Thank you from the above friends, so you can see that the +7 time zone
> of Hanoi has a longer history and maybe 1 time zone is Asia/Hanoi. If
> you live in Vietnam, you will clearly see the difference in time in
> Hanoi and HCMC, in the future when Vietnam is more developed, it may
> be necessary to adjust the HN and HCMC timezone. Paul Eggert, I know
> that there must be some rules for forming time zones. However, I see
> many exceptions such as Shanghai and Beijing, there are many other
> places that I have not mentioned. I think Hanoi too full of criteria
> for a time zone, or you can consider it an exception. Why not?
> Vào 16:48, Th 2, 18 thg 2, 2019 Phake Nick <c933103 at gmail.com
> <mailto:c933103 at gmail.com> đã viết:
>     Tz database does not deal with official timezone name. The time
>     used in Vietnam being named Hanoi time doesn't make it more Hanoi
>     than Ho Chi Minh as both should be using the same UTC+7 now. The
>     different was in 1970s. If your software is expected to show
>     official timezone name used in a region, then it's supposed to
>     translate Asia/Ho_Chi_Minh into "Hanoi Time"
>     On 2019-2-18 Mon 14:48, KP <khaiphan9x at gmail.com
>     <mailto:khaiphan9x at gmail.com>> wrote:
>     >So, I mean, +7 is now more standard time with Hanoi than Ho Chi
>     Minh City
>     -----
>     The thing is, the timezone history of Hanoi and Ho Chi Minh look
>     like this:
>     Hanoi: 1970-2019 UTC+7
>     Ho Chi Minh: 1970-1975 UTC+8 1975-2019 UTC+7
>     Bangkok: 1970-2019 UTC+7
>     Thus you can see the timezone history of Hanoi match the timezone
>     history of Bangkok from 1970 till now, while it doesn't match for
>     HCM City.
>     On 2019-2-18 Mon 16:53, Guy Harris <guy at alum.mit.edu
>     <mailto:guy at alum.mit.edu>> wrote:
>         On Feb 17, 2019, at 6:40 PM, Tim Parenti
>         <tim at timtimeonline.com <mailto:tim at timtimeonline.com>> wrote:
>         > As was discussed on the original thread in October 2014,
>         pre-unification time in Hanoi matches Asia/Bangkok since 1970
>         By which you presumably mean "from 1970 to 1976", because
>         "pre-unification time" ends when North and South Vietnam were
>         reunified in 1976.
>         > and thus is already considered covered by the database.
>         If *post*-unification time - which is post-1970 - doesn't
>         match Asia/Bangkok, then Asia/Bangkok should not be used for
>         any part of Vietnam; there should be one or more
>         Asia/{whatever} for Vietnam from 1970 to the present.
>         If Vietnam's pre-unification offset or rules were different
>         between the north and the south from 1970 to 1976, then "one
>         or more" means "at least two", e.g. Asia/Hanoi and
>         Asia/Ho_Chi_Minh (even if it was called Saigon in 1970).

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