Curious thing. The Chattahoochee River divides the US states of Alabama and Georgia, the former being on Central time and the latter being on Eastern time. There's a city in Georgia called Columbus, and it's right up against the river, and so is adjacent to Alabama and Central time.
Years ago we visited my wife's family in Columbus with some frequency, once we visited the Wal-Mart supercenter in Phenix City (yes, it's spelled way wrong) Alabama, which is right on the eastern border of Alabama, also next to the river. Since I worked in Wal-Mart Information Systems at the time, I had quite a bit of access and noted that the store's systems were on Eastern time, even though the entire state of Alabama is on Central.
Sure enough: https://en.wikipedia.org/wiki/Phenix_City,_Alabama "Phenix City lies immediately west across the Chattahoochee River from the much larger Columbus, Georgia and observes Eastern Time on a de facto basis (in contrast to the rest of Alabama, which observes Central Time) due to Phenix City's strong economic ties to Columbus."
The Olson Database is amazing; I've non-trivially interacted with it a number of times in my career.
Even so, the final, on the ground authority is the people who use and are affected by time zones.
Years ago we visited my wife's family in Columbus with some frequency, once we visited the Wal-Mart supercenter in Phenix City (yes, it's spelled way wrong) Alabama, which is right on the eastern border of Alabama, also next to the river. Since I worked in Wal-Mart Information Systems at the time, I had quite a bit of access and noted that the store's systems were on Eastern time, even though the entire state of Alabama is on Central.
Sure enough: https://en.wikipedia.org/wiki/Phenix_City,_Alabama "Phenix City lies immediately west across the Chattahoochee River from the much larger Columbus, Georgia and observes Eastern Time on a de facto basis (in contrast to the rest of Alabama, which observes Central Time) due to Phenix City's strong economic ties to Columbus."
The Olson Database is amazing; I've non-trivially interacted with it a number of times in my career.
Even so, the final, on the ground authority is the people who use and are affected by time zones.