Traveling across the line allows you to "repeat" a day.

The distance between meridians is widest at the equator (roughly 111 kilometres) and shrinks to zero at the poles.

Today, the meridian longitude remains as relevant as ever, though its application has evolved. Global Positioning Systems (GPS) use a "Reference Meridian" that differs slightly from the physical line at Greenwich due to shifts in tectonic plates and more precise satellite measurements. From the flight paths of commercial airliners to the data packets traveling through undersea fiber-optic cables, our entire global infrastructure relies on the mathematical certainty of these vertical lines. The meridian longitude is more than just a map coordinate; it is the universal language of space and time that connects every corner of the globe.