It only just hit me a month or two ago just what a timezone, as described by IANA, actually is.

I'm from the eastern half of the US state of North Dakota. We run on what we'd collloquially call "central time", often abbreviated CST. That's UTC-6:00 in winter and UTC-5:00 in summer (technically CDT, but whatever).

Long ago I had it passed down to me from on high that the IANA timezone indicator I should use for my local time is America/Chicago. Ok. Easy enough. Why Chicago, though? I long guessed because it happens to be one of the largest localities in the CST block? That is in fact the answer if you read the rationale of the tz database, but I did not know this at the time.

What threw me off, though, is that there are other localities that seemingly map to the same time zone block. Like America/Mexico_City, or America/Indianapolis. What's up with those? When I set my computer system clock to them, they behave just like America/Chicago does. Why are these here? And why these cities, specifically?

Then, imagine the loop I was thrown for when I discovered three timezone definitions exclusive to North Dakota. Those being America/North_Dakota/Beulah, ../../Center, and ../../New_Salem. What the fuck..?? These are literal nowhere towns. Midwest America is the middle of nowhere. North Dakota is the middle of nowhere within the Midwest. And these three towns are the middle of nowhere to the rest of us in North Dakota. What is going on? Why are there three tiny timezones in the middle of nowhere in the middle of nowhere in the middle of nowhere? And they're all right next to each other!

Then, it clicked. What do these three places have in common? These towns all used to be in the next timezone over ("Mountain Time", MST), but later decided to jump over to CST.

There's a humorous story for why this happened. Supposedly, drinkers in the capital city, Bismarck, would stay to bar close. Then, they'd all hop in their cars and drunk drive to the sister city across the river, Mandan, for an extra hour of fun, causing untold chaos in the process. The jump was allegedly to curb this. Sadly, that story apocryphal. In reality, it was just because it was economically favorable to be time-aligned with the state capital city. But I digress...

If you were, say, looking over historic records of events recorded in both Bismarck and Beulah, where records are always taken simultaneously, and your data happened to span back before this switchover, there would be an inexplicable point in time where after it the timestamps would match, but before it, they'd be offset. So, to encode that, Beulah gets its own unique timezone all to itself that indicates this historical switchover exists.

It also explains why there are three tiny timezones all right next to one another. Three counties participated in this switchover, and to make it happen, each one had to individually pass laws to enact it. These laws all took effect on slightly different dates. Thus, if we wish to capture the nuanced time shifts in all three counties, each county needs its own bespoke timezone.

IANA timezones aren't just representations of all the time zones that currently exist. They are representations of every unique permutation of historic clock changes for every place on Earth. That's fucking nuts! Knowing that, I went from being shocked that there are so many timezones to being shocked that the list of timezones is as short as it is!