Which city is used as the reference point for 0 degrees of longitude?

The imaginary line that divides the Earth into the Eastern and Western Hemispheres is known as the Prime Meridian. This globally recognized line of 0 degrees longitude runs directly through the Royal Observatory in Greenwich, a historic borough of London, England. All other lines of longitude, which are used to measure how far east or west a location is, are calculated from this specific starting point.

The selection of this London location was not arbitrary. It was officially established at the 1884 International Meridian Conference held in Washington, D.C. By the late 19th century, Great Britain was a dominant maritime power, and a vast majority of the world's sea charts and navigational maps already used Greenwich as their prime meridian. Choosing it as the international standard was a practical decision that aligned with existing global practices and recognized the Royal Observatory's leading role in astronomy (Deals) and timekeeping.

The significance of the Prime Meridian extends beyond just geography; it also serves as the anchor for global time. Coordinated Universal Time (UTC), the modern standard for world time, is based on the time at this meridian, evolving from the original Greenwich Mean Time (GMT). This means that every time zone on the planet is defined by its offset from the time in Greenwich, solidifying this single location's crucial role in how we map and measure our world.