Final answer:
Time zones are based on a theoretical division of the Earth's surface into 15-degree sections of longitude, corresponding to the Earth's rotation rate. However, actual time zone boundaries often diverge from these neat divisions and are adjusted for practical purposes to align with political, natural, or economic boundaries.
Step-by-step explanation:
In theory, time zones are established roughly every 15 degrees of longitude to correlate with the Earth's rotation rate of 15 degrees per hour. Since the Earth completes one rotation in 24 hours, this results in 24 time zones, each one theoretically 15 degrees wide. This means that ideally, the local time should be approximately the same within each time zone and the sun should be overhead at noon. However, in practice, the boundaries of time zones do not strictly adhere to this neat partitioning due to various practical considerations; they can zigzag to align with political borders, such as state lines, or natural features.
For instance, in the United States, time zones boundaries diverge significantly from the lines of longitude to accommodate regional and economic connections between areas. This results in time zones that are not exactly 15 degrees wide. Such adjustments are commonplace around the world to maintain a uniform time within regions. Conversely, countries like China have adopted a single time zone for the entire country despite it spanning the equivalent land area as the USA.
Therefore, while the concept of a time zone is based on a 15-degree division of the Earth's longitude, actual time zones are frequently adjusted to better serve the needs of the countries and regions they encompass.