The natural concept of time is solar time, which is based on the Sun’s position in the sky. But local solar time or local mean time varies by longitude. With the spread of railroads in the 19th century, there was a need for time zones to standardize time and simplify east and west travel.
The 1884 International Meridian Conference adopted a universal day beginning at Greenwich midnight, but did not specify any local times or time zones. Over the years since then each country has determined their own time zones, usually offset by one hour from Greenwich mean time (GMT), but in some cases offset by one-half or one-quarter hour.
If one travels far enough in an east or west direction, a time zone will be crossed. In general this differs from travel north or south. A traveler going west is said to gain time as the clock is turned back, and a traveler going east is said to lose time as the clock is moved forward. The difference in time between east-west travel and north-south travel shows that time is capable of having two dimensions.
Coordinated universal time (UTC) is based on International Atomic Time, which is a weighted average of the time kept by over 400 atomic clocks in over 50 national laboratories worldwide. This time convention does not vary by location.