[JJMcJ]

To some extent a compromise between solar time and political and economic realities. For example, the Eastern Time Zone in the USA stretches almost to 90 degrees West, reflecting the East Coast's powerful pull on that part of the country.

[WorldMaker]

A lot of it was GE's fault at the time, specifically. GE wanted facilities in New York, Cincinnati (OH), and Louisville (KY), among others, to all be in the same time zone and had the economic power at the time to lobby the railroads and the cities to make that happen.

[JJMcJ]

Friend told me that Indiana not adopting Daylight Time until quite recently was due to a struggle between broadcasters, who of course wanted to match their networks, and drive in operators, who wanted it to get dark earlier so they could start the shows earlier.

Way back when, the drive in people won out.

[WorldMaker]

Yeah, Indiana also had an interesting three way battle between Chicago, Louisville, and Indianapolis. A lot of population near Chicago getting Chicago broadcasts (Central), a lot of population near Louisville getting Louisville broadcasts (Eastern), with the state capital Indianapolis interestingly caught up in the middle (physically closer to Chicago, but maybe emotionally more connected to Louisville) which itself as a city eventually after a lot of back and forth settled on Eastern time following Louisville's lead as one of the westernmost cities in the timezone.

Indiana's Daylight Time mistakes were fascinating. It wasn't that the state didn't adopt it, it was that originally the state allowed it to be a per-county decision as timezones have always been in Indiana. At one point in time if you were traveling I-65 which is nearly due north/south between Louisville and Indianapolis you could experience four different timezones (CST, EST, CDT, and EDT) and which ones agreed with each other obviously depended on which month you were traveling. Since Indiana went state-wide Daylight Time and Indianapolis decided on EDT once and for all, all of I-65 today is EDT I believe, but it is still strange to remember the years where that wasn't the case.

(ETA: one of the underappreciated homogenizing factors here has been the modern cellphone. People would get really confused if their cellphones hopped an hour back/forth every so many miles as you passed county lines. In the eras of paper maps and hand-set clock radios in cars that would have mattered a lot less.)

[dron57]

The worst case is all of China being in the same time zone. It's quite crazy. China has about the same land area as the US.

[JJMcJ]

Western China has some kind of adjustments, only they don't call it a time zone. Don't know the details.