How are time zone borders decided and regulated?
The basis of time zones was to divide Earth into sections of longitude 15 degrees each. That would allow for 24 zones to represent 24 hours in the day (one rotation of Earth). However, in the United States, the borders were usually drawn to follow state lines, or natural landmarks and county lines. There are even a few instances of counties split into two time zones. Time zone boundaries can be legislated at the state and/or county level and also by the U. S. Department of Transportation. For more details on U.S. time zones, the federal law on time zones is defined in United States Code; Title 15 – Commerce and Trade; Chapter 6 – Weights and Measures and Standard Time; Subchapter IX – Standard Time; Sections 260-267. See United States Law on Standard Time, 15 U.S.C. ยง6(IX)(260-7). NIST is an agency of the United States Department of Commerce, and is not involved in the administration of time zones.
