Time Zones - Why do GPS Time Zone maps change so often?

 
CraigW's picture

Questions oftentimes arise here at the POI Factory when a GPS manufacturer offers a device update to GPS models that offer automatic time zone adjustments. The questions are typically along the lines of "Why is there a new time zone map? Time zones can't be changing this often (or at all)."

Time zones do change. Admittedly, changes in the USA don't occur too often but for folks who feel US time zones were carved in stone ages ago, just do an internet search for Indiana Time Zones—Wikipedia has a good summary.

I expect that most or all GPS manufacturers offering devices with a Time Zone map (needed for any GPS that offers automatic time zone adjustments) offer a global map, not one for the USA alone, and yes, time zone boundaries, dates, etc. do change—and with a speed that may make your head spin.

I take no credit for all that's offered in the links below and only post this FAQ to share the site where all is made clear to the best ability of its author.

A recent 2016 link to time zone changes recently made:

http://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-...

and the author's main "Time Site:"

http://codeofmatt.com/

From one of the author's posts:

Time Zone Characteristics

A time zone consists of all of the following:

-A geographic boundary that can usually be plotted on a map

-A legal name (or a common name), such as "Eastern Time"

-One or more rules which consist of:

--The effective date and time for the rule

--A standard offset from UTC, such as UTC-5

-If the time zone uses daylight saving time:

--The daylight offset, such as UTC-4. This is usually (but not always) one hour greater than the standard offset.

-The transition dates and times that daylight saving time starts and ends

I may be offering this FAQ since I live in Arizona near a single highway that changes time zones during Daylight Saving Time multiple times over a few hours' drive. I've also experienced time zone errors in the state during Daylight Saving Time around the North Rim of the Grand Canyon when cell phones state the wrong time meaning those with a dinner reservation at the Grand Canyon Lodge find they arrive for dinner at the wrong time of day if they trust their cell phone (not that different from voters recently in Turkey—see first link, above).