Talk:Time zone/Archive 3

The article states that

A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.

Time zones are defined as one or two offsets from Coordinated Universal Time (UTC), and (if two offsets are used) the days when the offset changes. Some time zones switch between offsets throughout the year due to daylight saving time (DST).

This seems to correspond to the notion of time zones as possibly being per-polity, so that, for example, the US states of Arizona and New Mexico are not in the same time zone, as (most of) Arizona does not observe DST, but New Mexico does.

However, the map at the top of the article, which is captioned "Time zones of the world", shows time zones defined only by the standard-time offset from UTC, so that Arizona and New Mexico are in the same time zone, the North American Mountain Time Zone.

The notion of time zone used in the tz database is closer to the first one, although that notion has to handle more than just standard and daylight saving time. For example:

• the rule that specifies when the offset changes can themselves change over time, and have changed in a lot of places, although, if "the days when the offset changes" refers to a set of rules for determining, for any given year, the days when the offset changes, that's handled by the definition above;
• Morocco adjusts its clocks for Ramadan;
• some entries in the tz database include the region the entry covers moving from one standard-time UTC offset from another.

See, for example, the map at the top of the tz database article, which is more complicated than the map at the top of time zone.

Some tz database documentation uses the term "timezone", with no space between "time" and "zone", to refer to the regions that a tz database entry covers, in a somewhat-subtle attempt to distinguish tz database entries from "time zones" in the sense in which "time zone" is used in the caption for the map. Guy Harris (talk) 22:24, 8 March 2024 (UTC)

@Guy Harris: I propose replacing the map with this SVG version that I recently made. It uses stripes for areas that observe two offsets, so it's closer to the definition in the article. In addition, this version uses intermediate colors instead of stripes for fractional hour offsets, which I think is clearer; lists the dates of offset changes below the map; uses less memory than the PNG version, without losing resolution; and can be edited more properly.

I think that the definition in the article already includes the case of Morocco. For clarity, I suggest changing the last sentence to: Some time zones switch between offsets throughout the year, usually due to daylight saving time (DST).

The tz database groups areas in the same time zone only if they have always shared the same time since 1970. But the map only considers what they currently observe. Heitordp (talk) 13:58, 10 March 2024 (UTC)

The proposed map applies to the "a zone represents a standard time offset from UTC" definition of "time zone", with stripes to indicate the portions of the zone where DST is observed"; it doesn't show differences between either current or past rules.

The article says

Time zones are defined as one or two offsets from Coordinated Universal Time (UTC), and (if two offsets are used) the days when the offset changes. Some time zones switch between offsets throughout the year due to daylight saving time (DST).

which covers Morocco in that it has two offsets; the second sentence doesn't say that the two offsets are necessarily due to DST, so that also can include the two offsets being due to Ramadan. Guy Harris (talk) 23:26, 10 March 2024 (UTC)

@Guy Harris: The map that I proposed does show the differences between current rules, as it lists the dates of offset changes for each area below the map. It doesn't show past rules, but I think that it would be impractical to do so. Heitordp (talk) 07:33, 17 March 2024 (UTC)

Morocco and Spain appear to be in the same "time zone" according to the map on time zone, but they aren't in the same tzdb timezone ("timezone", without a space between "time" and "zone"), as mainland Spain (Europe/Madrid) is currently following the EU DST rules, but Morocco (Africa/Casablanca) is currently following Morocco's Ramadan rules.

It's probably best not to even try to come up with a map for IANA time zone database timezones - if somebody wants that they should go to tz database and look at the map on that page - and decide what this page is to discuss, namely "offsets from UTC, "time zones" as most people think of them, or "timezones" (the term the tzdb documentation uses) or "tzdb regions" (the term I've used one occasions) meaning "everything that has its own tzdb ID". Guy Harris (talk) 08:20, 17 March 2024 (UTC)

Time zones are definitely regions, not offsets, as explained in the blog post cited in the article. But the exact regions that constitute the various time zones are not necessarily the ones in the tz database. It depends on which period is considered. The tz database considers all offsets used in each location since 1970, resulting in about 300 time zones (not counting aliases), most of which consist of smaller zones that only differed from larger ones many years ago. But that period is arbitrary. If we consider 1850, when each city used a different offset, there may be thousands of time zones. Conversely, if we consider 2024, there are only about 64 time zones, which are shown in the second map and table in the article. I think that the latter is what people mean when they speak of time zones. They still mean regions, but the ones that currently share the same time, possibly including currently scheduled changes such as DST but disregarding historical differences.

For this article, I suggest a simpler text that should fit any notion:

All time zones use offsets from Coordinated Universal Time (UTC). The offsets range from UTC−12:00 to UTC+14:00, and are usually a whole number of hours, but a few zones use offsets with an additional 30 or 45 minutes, such as in India and Nepal. Some areas use a different offset for part of the year, typically one hour ahead during spring and summer, a practice known as daylight saving time.

If the map is going to show each area with only one offset, I think that it makes more sense to show Morocco in UTC+1 because that's what it uses for almost the whole year, except one month. But I propose this map, which uses stripes for areas that use two offsets. Morocco is shown with stripes of UTC+1 and 0, and Spain with UTC+1 and +2, and below the map it lists the period when each place uses the second offset. I don't find the map of the tz database very useful, because it only shows the boundaries of time zones, but not what offsets they use. Heitordp (talk) 22:52, 19 March 2024 (UTC)

Time zones are definitely regions, not offsets, as explained in the blog post cited in the article. The US Standard Time Act of 1918 doesn't use the term "time zone", but does speak of "the territory of continental United States" being "divided into five zones", with each zone being given specific "standard time"s, and specifying that each zone's time gets "advanced one hour" "at two o'clock antemeridian of the last Sunday. in March of each year" and "by the retarding of one hour, [returned] to the mean astronomical time of the degree of longitude governing said zone" "at two o'clock antemeridian of the last Sunday in October in each year". So those zones have both geographical boundaries "defined by an order of the Interstate Commerce Commission" and standard time offsets.^[1] The DST part of the Standard Time Act was repealed in 1919; the term used was, again, just "zone". In practice, some places adjusted the clocks twice a year and some didn't; it was not zone-dependent - one place within a zone might observe DST and another place might not, so, while a given zone has a specific standard time offset, the rules for adjusting the offset may differ between places in the zone.

The Uniform Time Act of 1966 re-standardized DST, as well as adding more zones; the terminology remained "zone". It allowed states to opt out of DST - Arizona did so - but did not give states that did so separate zones, so a "zone", in US law, has geographical boundaries and a single standard time offset from UTC, but does not have a single set of time-change rules, so a "zone" does not correspond to a tzdb "timezone"/region. In particular, both Arizona. which does not observe DST, and New Mexico, which does, are in the same "zone" which, to use the terminology of the Standard Time Act of 1918, has, as its "standard time", a time that is "known and designated as United States Standard Mountain Time". That zone is generally called the Mountain Time Zone, although it appears that the name "Mountain Time Zone" - and the other such names - aren't specified, as such, in US law.

As far as I know, when people speak of "time zones" in the US, they're speaking of the zones as established by the aforementioned acts, meaning that, for example, both Arizona and New Mexico are in the "Mountain Time Zone", not in separate zones.

Canada appears to have set up standard time with the Reckoning of Time Act in 1890, which specified the standard times of specified provinces and territories, rather than specifying "zones" in the US sense.

In that blog post, Denver Hamilton might be arguing that people talking about times on computers use the term "time zone" to refer to tzdb timezones/regions, rather than to "zones" in the US sense, but he also acknowledges that "zones" in the US sense "are also called “time zones” in casual conversation". I don't think Wikipedia will be all that successful to get people to talk about, for example, the America/New_York time zone rather than the Eastern time zone, so the time zone page will have to deal with the common use of "time zone".

I think that the latter is what people mean when they speak of time zones. They still mean regions, but the ones that currently share the same time, possibly including currently scheduled changes such as DST but disregarding historical differences. Again, as far as I know, people think of both Arizona and New Mexico as being in the Mountain Time Zone even though their clocks don't always agree - it's more like "Arizona and New Mexico are in the Mountain Time zone, but Arizona doesn't do DST while New Mexico does", so it's more like "currently share the same standard time offset". That wouldn't correspond to the tzdb even if the tzdb combined all locations with the same offset and rules since 2024-01-01, as that tzdb would have Arizona and New Mexico in separate tzdb regions/timezones.

And, on top of that, a tzdb region/timezone doesn't necessarily have a single standard time offset - the standard time offset of a location may change for various reasons, including "state/province/etc. X moved to a different standard time offset" (which has happened) and "country X seized that location from country Y, or that location left country Y and joined country X or became a new country Z, and the standard time offset was changed", and so on. The blog post in question mentions Coral Harbour; see {{section linkTime in Nunavut#History]] for what happened (which does not appear to be in the tzdb - I'll mention that on the tz mailing list) - that's one case of "moved to a different standard time offset".

The online Merriam-Webster Dictionary says that "time zone" means "a geographic region within which the same standard time is used". A Google search for "definition" "time zone" shows a definition from "Oxford Languages" stating that a time zone is "a range of longitudes where a common standard time is used". This, again, suggests that the common meaning of "time zone" has nothing to do with time adjustments, it's just "a region with a given standard time offset".

So tzdb regions/timezones will probably forever remain different, at least for some locales, from what many people think of as a "time zone".

So I'd use

A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.

Time zones are defined by the standard time offset from Coordinated Universal Time (UTC). Some locations within a time zone may adjust the clock during the year. For example, locations may switch between offsets throughout the year due to daylight saving time (DST). The UTC offsets range from UTC−12:00 to UTC+14:00, and are usually a whole number of hours, but a few zones are offset by an additional 30 or 45 minutes (such as in India, South Australia and Nepal).

as the beginning of the article, dropping the notion that DST rules are part of a time zone.

I don't find the map of the tz database very useful, because it only shows the boundaries of time zones, but not what offsets they use. It's more than just offsets, it's offsets and when various offsets were, or will be, in effect. I suspect a map that shows all that information would be complicated enough to make readers' eyes bleed. Guy Harris (talk) 03:59, 20 March 2024 (UTC)

I agree with everything that you wrote. Feel free to change the text in the article as you proposed.

What do you think about changing the map to this version that uses stripes for areas with DST? I think that it still matches the text that you proposed, as it shows the boundaries between time zones based on standard time, but it's more accurate for the purpose of showing the offset used in a location. Heitordp (talk) 10:42, 24 March 2024 (UTC)

It appears that Morocco is striped, so it doesn't only use stripes for areas with DST, it uses stripes for areas that adjust their time away from standard time during the year, whether or not that's DST, which is the right thing to do. I.e. not all adjustments away from standard time are for DST.

So that map would be appropriate. Guy Harris (talk) 17:26, 24 March 2024 (UTC)

This edit request to Time zone has been answered. Set the |answered= parameter to no to reactivate your request.

2601:447:CA83:8760:F928:602D:BFBE:BC32 (talk) 22:39, 5 April 2024 (UTC)

No request made so request denied. Jc3s5h (talk) 22:46, 5 April 2024 (UTC)

copied from your own page on Madras Time to be added to the history section. Other countries are mentioned and this was the first in 1802 2A02:C7C:3765:1C00:F3B9:BC52:375F:1AB7 (talk) 11:20, 12 May 2024 (UTC)