Exceptions, Oddities and Notes
A word about standards. All time zones world wide are based on offset from the Prime Meridian, also known as the Greenwich Meridian. That is the line that runs from the north to the south pole at longitude 0°. No matter what you call it, it passes through the Royal Observatory in Greenwich, England. Thus "Greenwich Mean Time".
In research literature and in cyberspace you will find Greenwich Mean Time referred to in many different ways, usually GMT, UTC (Coordinated Universal Time), or Zulu time. Military and Aviation usually use Zulu, or just Z.
Here at OnTimeZone.com we use GMT, because that is what travelers seem most familiar with. Time geeks (they walk among us) will prefer you use UTC when conversing on the time related topics. And truly there are small technical differences between UTC and GMT, but travelers need not concern themselves about it.
Time zones are fundamentally based on 24 imaginary wedges running from pole to pole at 15 degree increments, beginning centered on longitude 0°. Starting with an offset of zero hours for that first "slice" (which occupies the longitude from -7.5° to +7.5°) heading eastward, for each 15° wedge you add 1 hour for each zone, and heading westward you subtract 1 hour for each zone. They meet on the other side of the globe at the fundamental basis of the International Date Line, the imaginary line that runs from pole to pole at the 180° longitude.
In reality, actual time zone lines deviate (often radically) from their fundamental basis. Politics, history, commerce, and sometimes forces that defy rational explanation all combine to influence the real time zone borders.
The International Date Line itself is similarly influenced, following a ragged path roughly centered at 180° longitude. Crossing it traveling eastward you subtract 24 hours, and if traveling westward you add 24 hours. Simple :)
Most time zones are offset from GMT in whole 1-hour increments. A few offset from GMT in fractions of an hour -- most of those by half hour, a few by a quarter of an hour.
Forward thinkers want to end the madness. Click here to see their their elegant solution.
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 governmental entities -- 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 the exceptions that made their way into the boundaries at OnTimeZone.com:
NV: In northern Elko County Nevada Jackpot, Jarbridge, 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.
NM: Nara Visa New Mexico observes Central time though they are officially in the Mountain zone.
TX: The NW Corner of Culburson County Texas, near and including Quadalupe Mountains National Park, observes Central time though they are officially in the Mountain zone. Even the National Park observes Central time, an oddity itself in that federal facilities rarely follow local unnoficial exceptions. This exception is so firmly entrenched in the area that it is widely mistaken as official. The distance to which the observance of this exception extends south and east of Hwy 180 is arbitrary. That part of the county is sparsely populated and appears to have no services, so the point is somewhat moot.
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.
Our data presumes that by default most North American locations follow DST (not necessarily on the same schedule). Exeptions are discussed below:
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) have a mix of DST observance, and the situation sometimes changes with little notice. Cuba, the Bahamas and the Turks and Caicos Islands currently observe DST. As of this writing the Cayman Islands are studying a possible shift to observe DST.
Cuba has been changing their clocks on the same dates as the U.S., etc., since 2013, but their changes happen at midnight standard time -- midnight CUST(EST) & 1 AM CUDT(EDT).
Though Bermuda is not technically part of North America, and is well north of the Caribbean, it is worth noting that it also follows DST, on the US/Canada schedule.
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. As of 2014 Haiti still observes DST and apparently intends to for the near future. It may be best to check first if it matters to you.
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 last Sunday in October. All EU countries shift at the same moment (1AM GMT) no matter what time zone that country observes.
The borders in OnTimeZone.com were drawn primarily for road travelers. Little attempt is made for precision over roadless areas or over water. This is not focused to benefit 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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