A geographical region throughout which civil time is reckoned to be the same. Time zones are based on longitude bands 15° wide, corresponding to a one-hour difference in local time. There are, however, considerable deviations from regular lines of longitude in the boundaries of time zones in order to take account of the distribution of land over the Earth’s surface and the locations of centres of habitation. The difference between most adjacent time zones is one hour, but there are some instances of half-hour differences aimed at minimizing deviations from local time.