Look a little closer
Time-zone borders zigzag because clock time is not a purely astronomical grid based on longitude. It is a social system: it roughly follows the Sun while bending around countries and communities so people can share practical schedules.
Earth rotates about 360 degrees in 24 hours, so a simple division gives each zone an average width of 15 degrees of longitude. Theoretical borders would be straight north-south lines, but those lines could split a city, state or connected economic region between two clocks.
Before railways and telegraphs spread in the nineteenth century, towns could keep local solar time, setting noon near the moment the Sun stood highest. Faster travel and communication made many local timetables difficult to coordinate, increasing the value of shared standard time.
Governments therefore define time zones through law and administration. Boundaries may follow states, provinces, counties, mountains or rivers that people can recognize. Commuting, trade, broadcasts, schools and ties with neighboring areas can matter more than a geometrically straight meridian.
Offsets are not always whole hours. Some countries choose half-hour or 45-minute differences, and some large nations keep one time across a broad span of longitude. The International Date Line also bends widely to avoid dividing islands and countries between two calendar dates.
A time-zone map is thus Earth's rotation overlaid with political and everyday choices. Borders and daylight-saving rules can change, so real schedules and computer systems need current time-zone data rather than a permanently fixed geometric map.
