Which line of longitude was internationally adopted as the prime meridian in 1884?

The Greenwich Meridian was internationally adopted as the prime meridian in 1884.

The line passes through the Royal Observatory in Greenwich, London, and is defined as 0 degrees longitude. It became the reference from which longitude is measured eastward and westward around Earth.

Delegates at the International Meridian Conference in Washington, D.C., voted in 1884 to select Greenwich as the global reference. Britain’s extensive maritime charts and the widespread use of Greenwich-based timekeeping strongly influenced the decision. Twenty-two nations participated, and the motion passed by a large majority.

Modern satellite-based coordinate systems use a slightly different geodetic reference line, because Earth is not a perfect sphere and the old observatory’s position is affected by local measurements. Nevertheless, the Greenwich Meridian remains the historic and widely recognized name for the zero-longitude line.