Exceptions, Oddities and Notes
A word about standards - all time zones world wide are offset from Greenwich Mean Time. This is the time at longitude zero degrees, also known as the Greenwich Meridian or Prime Meridian, which (by amazing cooincidence) passes through the Royal Observatory in Greenwich, England.
In research literature and in cyberspace you will find Greenwich Mean Time referred to in many different ways, usually GMT, UTC (Coordinated Universal Time), and Zulu time. Military and Aviation usually use Zulu, or just Z.
Here at OnTimeZone.com we use GMT, because that is what normal folks are most familiar with. Time geeks (they are out there) will prefer you use UTC when conversing on the time related topics.
With much more exception than rule, 24 standard time zones run from pole to pole at 15 degree increments, heading east from the Greenwich Meridian, adding 1 hour for each zone East of GMT, and subtracting 1hour for each of the 12 zones West of GMT. In the middle, they meet at the International Date Line roughly near 180 degrees longitude, where if traveling east you subtract 24 hours, and if traveling west you add 24 hours. Simple :)
North America's nine time zones, being in the Western hemisphere, are offset from GMT in negative increments, as seen here:
Wherever locally "observed" time differs from official, the main borders in OnTimeZone.com follow the observed time - which is what a traveler is likely to actually encounter.
A problem with that is that unofficial "observed" differences typically follow vague areas of economic or political influence which defy precise definition. But we had to draw them somewhere. Usually these borders are in very lightly settled areas - and we took pains to draw them on the correct side of any area which may have businesses or services. That was our intent anyway - corrections appreciated!
Wherever these areas are in the US, unofficial borders are drawn in green, for reference purposes. No attempt was made to do this for other countries, because distinctions between official and unofficial blur a bit in the various political subdivisions within most countries. In the US all official time zone borders are well and clearly documented by a single source - the US Dept. of Transportation.
But be aware that within an area where observed practice differs from official, there are often internal exceptions such as Polling places, Post Offices or other federal offices, and sometimes law enforcement or various other levels of government -- who may observe official time even if the rest of the community does not.
Bars or liquor stores in these areas are often required by law to observe official time. This can provide quite an advantage for properly situated bars, when last-call sojourners migrate across an official time zone border to cadge one more hour of bliss.
Here are some of the exceptions that made their way into our boundaries:
NV: In northern Elko County Nevada Jackpot, Owyhee, Mountain City, and the Duck Valley Indian Reservation all observe Mountain time though they are officially in the Pacific zone.
NV: West Wendover Nevada is officially in the Mountain Time zone.
OK: Kenton Oklahoma observes Mountain time though they are officially in the Central zone.
AL: Phenix City Alabama (no, that's not a typo... though it may have started out that way - but maybe not) and the area witin a 10-15 mile radius on the AL side of the state border observes Eastern time, even though they are officially in the Central time zone.
AK: Hyder Alaska unofficially observes Pacific time, even though they are officially in the Alaska time zone. But the post office, being a federal facility, is on Alaska time.
AK: The Annette Island Indian Reservation near the southern tip of Alaska observes GMT-8, the same as Pacific Standard time, year round. It does not observe Daylight Saving time. So in the winter it matches British Columbia, and in the summer it matches Alaska.
SD: The city of Fort Pierre South Dakota (legally in the Mountain time zone) and a large radius on the west side of the Mountain/Central border observes Central time. Research determined that the distance this observance extends to the west is a matter of disagreement among the locals. After some effort to get a definitive answer I gave up and arbitrarily selected 20 miles, though I heard credible opinions that it stretched out as much as 50 miles. There are no services and very few residents in the western part of Stanley county, so the point is somewhat moot.
CA: Winterhaven California, in deference to its proximity to Yuma AZ, observes Mountain Standard Time year round. This means that (like AZ) Winterhaven does not observe Daylight Saving time. So this puts Winterhaven ahead of California by one hour (in sync with Arizona) during Standard time - in the Fall and Winter. And in sync with both CA and AZ during Spring and Summer (Daylight Saving time). The dividing line of this observed boundary is locally considered to be the border of the Fort Yuma-Quechan Indian Reservation.
CA: Earp/Vidal California, in deference to its proximity to Parker AZ, observes Mountain Standard Time year round. This means that Earp and the surrounding area does not observe Daylight Saving time. So this puts Earp ahead of CA by one hour (in sync with AZ) during Standard time - in the Fall and Winter. And in sync with both CA and AZ during Spring and Summer (Daylight Saving time). The dividing line of this observed boundary is estimated, but it is reported to extend to somewhere between Vidal and Vidal Junction.
Saskatchewan: Two things are odd about the time in the province of Saskatchewan. Firstly, it observes Central Time instead of the Mountain Time Zone in which most of it geographically resides. Secondly, it does not observe Daylight Saving time, remaining on Central Standard time (GMT-6) year round. There are a couple of exceptions in border areas - see below.
Saskatchewan: The western city of Lloydminster area, which straddles the provincial border with Alberta, officially observes Mountain Time including Daylight Saving time
Saskatchewan: The eastern towns of Denare Beach and Creighton which are near the provincial border with Manitoba, observe Daylight Saving time.
British Columbia: The Peace River area (a large chunk of east-central BC) observes Mountain Standard time year round, and does not observe Daylight Saving time. This includes Dawson Creek, Fort St. John and the surrounding area. So in Spring/Summer they are in sync with the rest of BC (which observes Pacific Daylight time). But in the winter they instead sync up with their neighbors to the east in Alberta.
Quebec: The eastern end of Anticosti Island, and that portion of mainland Quebec laying north of the island and west of the Natashquan river, now officially observe Eastern time.
Ontario: Southern Ontario, west of Thunder Bay, an area including Upsala, Shebandowan and Atikokan locally observes Eastern time even though they lie in the Central time zone. Also, the Atikokan portion of this area, including Quetico Provincial Park, does not observe Daylight Saving time, though in some descriptions they are said to observe Central Daylight time year round - which is the same thing in wall clock time..
Ontario: The towns of Pickle Lake and New Osnaburgh do not observe Daylight Saving time.
Ontario: The "Big Trout Lake" area observes Central time. The border is drawn by estimate.
Nunavut: Though the community of Arctic Bay on the western edge of Baffin Island is technically in the Central Time zone, it observes Eastern time to keep in sync with the bulk of the island.
Nayarit: This Mexican state is in the Mountain time zone, but in April 2010, Bahia de Banderas at its southern tip officially shifted into the Central time zone to join Puerto Vallarta across the border in the state of Jalisco.
The Aleutian Islands of Tommorow (or yesterday?)
Daylight Saving Time (explained!)
Note: Frequently referred to as Daylight Savings Time, which is incorrect. It's "saving", not "savings".
US and Canada: DST starts 2AM the second Sunday in March, and ends at 2AM the first Sunday in November.
Hawaii does not observe Daylight Saving time.
Indiana: As of 2005, the whole state observes Daylight Saving time. Prior to that only parts of the Hoosier state observed DST.
Newfoundland/Labrador: As of the Spring of 2011, Newfoundland officially shifted their Daylight Saving Time transition to 2AM. Prior to that Newfie DST started and ended at 12:01 AM, 119 minutes earlier than the rest of Canada and the US. So before 2011, when Newfies returned to Standard Time in the Fall, at one minute after midnight Sunday morning they not only changed time, they changed date - reverting back to 11:01PM Saturday. I can't imagine why they did that, but I am fairly certain the computer geeks were not consulted.
St. Pierre and Miquelon: These islands off the coast of Newfoundland are French, and thus part of the EU. They have their own time zone. However, they follow Canadian DST date and time observance, not EU (European Union) dates and times, which are different.
Mexico: Except for 10 border towns which officially follow the US DST schedule (Tijuana, Mexicali, Ciudad Juarez, Ojinaga, Ciudad Acuña, Piedras Negras, Anáhuac, Nuevo Laredo, Reynosa and Matamoros), Mexico starts DST at 2AM on the first Sunday in April (3 or 4 weeks before the US), returning to Standard time at 2AM on the last Sunday in October (one week before the US). This causes a temporary difference between US and Mexican time even in the same time zone. The state of Sonora does not observe DST at all, in sync with Arizona - its northern neighbor.
Mexico/Oaxaca: Most municipalities in the southern Mexican state of Oaxaca refuse to honor DST. This is an ongoing dispute with their federal government and may change. These Oaxacan DST exceptions are not documented and thus are NOT reflected in the OnTimeZone.com data.
Central American countries including Belize and Guatemala which are on Mexico's southern border, do not observe Daylight Saving time. Thus, in the Summer time (DST), there is a time transition between Mexico and it's southern neighbors - reflected in light blue on the map. The next time zone to the south is the Central/Eastern time zone border between Panama and Costa Rica. Because neither observes DST, the time transition at their border is year-round and remains drawn in magenta. So during DST, departing that that portion of Central America north of Panama you jump forward an hour no matter whether you are heading north into Mexico, or south into Panama.
Caribbean and Central American islands (we concern ourselves only with those in the Eastern and Atlantic time zones) typically do not observe DST, though changes in observation are not rare. Cuba currently observes DST. As of this writing the Cayman Islands are studying a possible shift to observe DST.
Haiti: Haiti has an erratic history of DST observance. They observed it 1983-1997 and 2005-2006. At the last moment they announced a return to DST observance (using the US/Canadian shedule) in 2012. During DST, this restores them to being the same local time as their neigbors, the Dominican Republic, with whom they share the island of La Hispaniola. Haiti is on Eastern time. The Dominican Republic is on Atlantic time and does not observe DST. So they will be in sync (GMT-4) in Spring/Summer, and Haiti will be an hour behind in Fall/Winter. It is certainly too soon to guess if Haiti will continue to follow DST beyond 2012.
European Union: Though outside our area of focus, it may be useful to keep in mind that the EU differs from North America by observing DST from the last Sunday in March to the first Sunday in November. Another difference is that it all EU countries shift at the same moment (1AM GMT) no matter what time zone that country is in.
The borders in OnTimeZone.com were drawn primarily for road travelers. Little attempt was made for precision over roadless areas or over water for the benefit of offroad travlers, aviators or sailors. I did take care to keep the line on the correct side of any inhabited islands.
Wherever the real time zone border follows an irregular boundary such as a river or a ridge, I did not try to exactly mimic the boundary - which would have taken too many data points. Instead I generally tried to keep the line simple while not letting it touch or cross any roads except at the correct points where that road actually does cross or touch the real time zone boundary. So it may look a bit "low res" when you are zoomed way in, but there (hopefully) should be no instances where any part of a road is on the wrong side of a time zone border line.
For a description of just how difficult dealing with time zones can be, watch this youtube video. It will make you laugh, and leave you sympathetic to those who need to worry about such things.
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