Why time-zone borders bend around people
If time were set strictly by the Sun, each 15 degrees of longitude would make a neat one-hour band: Earth turns about 15 degrees in an hour. But a clock is also a civic rule. Governments choose a standard time for places they administer, and they generally have practical reasons to keep nearby communities on the same clock.
A straight longitude line can cut through a city, a state, or a region whose residents share schools, workplaces, markets, and public services. A boundary that follows an administrative border—or curves around a populated area—can spare people the confusion of using different times for short trips. The tradeoff is that the clock may be less closely matched to local daylight.
One clock can serve a very wide country
India uses a single standard time across a country that stretches far from east to west. That choice makes national schedules easier to coordinate, but sunrise and sunset occur at noticeably different local times in its western and eastern regions. Other countries use multiple time zones when the benefits of closer alignment with daylight outweigh the cost of coordinating across them.
There is no single global authority that draws every time-zone boundary. International conventions help countries coordinate, but governments decide which standard time applies within their borders. For a traveler, that means a time-zone map is not just a diagram of Earth’s rotation: it also records choices about which communities and schedules should stay together.
