Therefore, to maintain uniformity and ease of transport, communication and for other practical purposes, there has to be a common standard of time, at least in one considerable extent of space, such as administrative divisions, regions, or individual countries. The Standard Time Zone of World Map is thus very helpful.
The present world time zone map uses 24 standard meridians of longitude that run from the North Pole to the South Pole, at right angles to the equator, and are 150apart, starting from the prime meridian or 00 longitude that passes through Greenwich near London, England. These meridians are therefore, theoretically speaking, the centers of the 24 standard time zones. Each 150 zone to the east or west of the initial 00 zone is therefore represented by one hour.
However, in practice these zones are not sacrosanct and are altered or subdivided, for convenience's sake, by individual countries that fall within them. For instance, in China, there is only one time zone for the whole country, whereas the USA is divided into six time zones. Similarly, the International Date Line is extended eastwards around the Pacific island country of Kiribati to avoid cutting through it so that one uniform date could be maintained for the whole country on one particular day.
