[PeterHolzwarth]

My goodness, I didn't realize how many states are dual time zone. Florida, Oregon, Idaho, both of the Dakotas, and many more - I assume there's a historical reason for each, but that has got to play havoc with things at the state administrative level.

And look at Michigan - given the odd spatial realities of the state, that's just bloody minded. I didn't realize Arizona was that county-by-county nuanced: I assumed the whole state did its own "screw clock changes" thing (tho the oddity of Wendover, a recent change, makes sense). And Puerto Rico looks to be doing Eastern time merely out of politeness.

[icegreentea2]

This map which combines population density and time zones makes some of the decisions more clear I think - https://www.reddit.com/r/MapPorn/comments/7vvlgz/contiguous_...

The reality is that a lot of counties/areas in one state are significantly more economically integrated (or drawn to, or dependent) to areas in other states. This can result in border regions swapping time zones.

For example, the 4 Michigan states you highlighted - given the reality of UP, those areas probably interact with Wisconsin probably even more than the rest of the UP. You see similar population clusterings on the WA/MT and OR/ID borders.

[giraffe_lady]

A lot of times it is simply following some geographic boundary that is obvious locally but not on a map like this: a river or whatever. Even if the boundary isn't itself a major obstacle now the settlement history is embedded in the social geography.

Or like look at that corner of northern indiana. That's the part of indiana that is part of the chicago metro area. Makes absolute sense to avoid cross-timezone commutes.

Northern michigan is pretty damn far north! Winter sunsets up there would be before 4pm on central time. Makes sense for them to shift it permanently.

I think they probably all make sense if you know how to look at them right.

[PeterHolzwarth]

Yeah, good point - I assume a lot of the seeming anomalies are due to conurbations that, as you say, aren't obvious when just looking at borders.

[nocoiner]

But Puerto Rico isn’t on eastern time. And I think the exceptions in Arizona are reservations and tribal land.