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Map Layer Info

Time Zones of the United States

What this map layer shows:

The six standard time zones for the United States and a seventh zone which encompasses Puerto Rico and the U.S. Virgin Islands as of 2010.
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Background Information
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The railroads instituted standard time in time zones in the United States and Canada on November 18, 1883. Before then, most cities and towns used local solar time maintained by some well-known clock, such as one on a church steeple. After the railroads were built, allowing rapid travel across great distances, their efficient operation required the standardization of time in zones.

The Act of March 19, 1918, sometimes called the Standard Time Act, established standard time in time zones in U.S. law. The Standard Time Act also established daylight saving time (DST), which was repealed in 1919 but was reestablished nationally during World War II. After the war, the use of DST varied among States and localities. The Uniform Time Act of 1966 provided standardization of the dates when DST begins and ends each year but allowed for local exemptions from its observance.

The Interstate Commerce Commission (ICC) initially had the authority over time zone boundaries. Congress has since transferred boundary authority to the U.S. Department of Transportation (DOT), and the boundaries are defined in Code of Federal Regulations, Title 49--Transportation, Subtitle A-- Office of the Secretary of Transportation, Part 71--Standard Time Zone Boundaries.

Further information on the history of time zones in the United States is available from the U.S. Naval Observatory Astronomical Applications Department time zones page.

The Time Zones of the United States map layer shows the six standard time zones for the United States, and a seventh zone, which encompasses Puerto Rico and the U.S. Virgin Islands. Also shown are the areas in each zone that do not observe DST. Additional descriptive information includes the zone name and the offset from Coordinated Universal Time (Greenwich mean time). Time zone boundaries are current as of 2010, but they do change. See govpulse for any changes since then. This map layer was compiled by the U.S. Geological Survey.


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