How are time zones determined?

Different countries have different time. How are these determined? Is there a timer in a particular place where everyone's time is based?

it is based on the time that the sun is out for a certain amount of time in different regions of the world.

Coordinated Universal Time (UTC) is a high-precision atomic time standard. UTC has uniform seconds defined by International Atomic Time (TAI), with leap seconds announced at irregular intervals to compensate for the earth's slowing rotation and other discrepancies. Leap seconds allow UTC to closely track Universal Time (UT), a time standard based not on the uniform passage of seconds, but on Earth's angular rotation.

Time zones around the world are expressed as positive or negative offsets from UTC. As the zero-point reference, UTC is also referred to as Zulu time (Z). UTC is often referred to as Greenwich Mean Time when describing time zones.

the ans is yes there is a place where a particular time is fixed and according to that all the other world's time are takn into consideration ,,,,which GMT in grear britain (UK),,It ia old histirocal tower watch which is the standard time and all the time zones are manage + or - or according to that...