[tz] How can I add a new time zone: 'America/Joao Pessoa'?

Tim Parenti tim at timtimeonline.com
Sun Jan 31 23:14:06 UTC 2021


On Sun, 31 Jan 2021 at 17:40, Fabrício Cabral <fabriciofx at gmail.com> wrote:

> America/Fortaleza is further than America/Recife. So, by logic, Joao
> Pessoa people choose America/Recife instead of America/Fortaleza.

For recent and current timestamps, there is no difference between
America/Fortaleza and America/Recife.  Both of those entries have used
UTC-03 year-round since October 2002.

The only modern timestamps for which these two entries differ is over one
week in the October 2000, when Pernambuco appears to have ended Daylight
Saving Time after one week while Paraíba and other neighboring states ended
it after two weeks.  This difference is shown in lines 983–1000 of the
'southamerica' file in version 2021a.

# Maranhão (MA), Piauí (PI), Ceará (CE), Rio Grande do Norte (RN),
# Paraíba (PB)
Zone America/Fortaleza  -2:34:00 -      LMT     1914
                        -3:00   Brazil  -03/-02 1990 Sep 17
                        -3:00   -       -03     1999 Sep 30
                        -3:00   Brazil  -03/-02 2000 Oct 22
                        -3:00   -       -03     2001 Sep 13
                        -3:00   Brazil  -03/-02 2002 Oct  1
                        -3:00   -       -03
# Pernambuco (PE) (except Atlantic islands)
Zone America/Recife     -2:19:36 -      LMT     1914
                        -3:00   Brazil  -03/-02 1990 Sep 17
                        -3:00   -       -03     1999 Sep 30
                        -3:00   Brazil  -03/-02 2000 Oct 15
                        -3:00   -       -03     2001 Sep 13
                        -3:00   Brazil  -03/-02 2002 Oct  1
                        -3:00   -       -03

This difference of one hour for one week in 2000 is the reason that
America/Fortaleza and America/Recife are separate entries in our database,
so technically America/Fortaleza is more correct to use for João Pessoa,
but there is otherwise no difference since 1914.

Please see our project's guidelines for creating new timezone identifier
In particular, among our goals are to "[u]niquely identify every timezone
where clocks have agreed since 1970", which means that "[i]f all the clocks
in a timezone have agreed since 1970, [we] do not bother to include more
than one timezone".  Notably, a city being large or being a capital of a
region or country is not sufficient for us to add a new entry.  The United
States, for example, is mostly covered by a small handful of entries, and
many US states do not have separate entries of their own as they have
always matched neighboring states since 1970.

The time zone changes are the same of America/Fortaleza

The listing above shows that our records agree that clocks in João Pessoa
and the state of Paraíba have matched clocks in Fortaleza, the state of
Ceará, and several other neighboring areas since 1914, which is well before
our 1970 cutoff.  If that information is incorrect, we'd be happy to hear
of reliable references to support a proposed change.  But otherwise, we're
unlikely to add a separate America/Joao_Pessoa entry.

Tim Parenti

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