Time zones
Why are time-zone borders crooked?
The textbook picture of 24 straight strips is a useful starting point. Real civil time follows communities, borders, trade and law.
Fifteen degrees is only the ideal
Earth turns 360 degrees in roughly 24 hours, so a one-hour zone is 15 degrees wide on average. That is a geometric convenience, not a rule that communities must follow.
Shared daily life matters more than longitude
A region may choose the clock used by a capital, trading partner or neighbouring administrative area. In the United States, many boundaries follow counties; elsewhere borders bend so a country or island group can share a date and working day.
A map is a snapshot of decisions
Time-zone boundaries and daylight-saving rules are changed by political bodies. Software therefore uses a rules database rather than calculating a zone from longitude alone. A coordinate lookup is useful, but the legal clock still has the final say.