How are time zones decided?

Time zones are primarily determined by political and administrative decisions made by individual countries or regions rather than strictly by geographic or longitudinal lines. While the Earth is naturally divided into 24 time zones based on 15-degree increments of longitude (each representing one hour difference), the actual boundaries of time zones often deviate from this ideal for practical reasons. National governments decide where their time zones begin and end to best fit their social, economic, and political needs. For example, a country might choose to have a single time zone across its entire territory for convenience, even if it spans multiple natural longitudinal zones, or it might split into multiple time zones to better align with daylight hours. Additionally, borders between time zones often follow political boundaries such as country or state lines to avoid confusion within jurisdictions. The irregular shapes of some time zones arise because countries want to align local time with social activities, business hours, or daylight patterns. Geographic features like mountains, rivers, or population centers can also influence these boundaries. Some regions adopt half-hour or 45-minute offsets to better suit their specific needs, leading to further irregularities. In short, time zones are a human convention designed to balance the natural solar time with the practicalities of modern life, and their boundaries reflect a mix of geography, politics, and culture.