The World Standard Time Zone Maps digital collection provides access to maps dating back to 1944 showing the standard time zones of the United States and for each country and continent. All nations use standard time zones based on degrees of longitude for commercial purposes, although individual countries use half-hour and quarter-hour deviations. The maps depict the changes in time zones over the ages—for example, China currently uses a single time zone in spite of its large geographic size. Prior to 1949, China used five time zones.
Geography Lesson: World Time Zones
GIS Research and Map Collection