The 1884 International Meridian Conference selected the Greenwich meridian as the for longitude.
Your smartphone doesn’t "look up" longitude; it calculates it using atomic clocks on 31 satellites. Each satellite constantly broadcasts its position and precise time. Your receiver compares the time difference between several satellites to triangulate your longitude and latitude to within centimeters. meridian longitude
So, the next time you check your watch, remember: somewhere, a meridian is crossing your location, linking you directly to the North Pole, the South Pole, and the historic observatory at Greenwich. a meridian is crossing your location
Meridian Longitude: The Invisible Lines That Define Our World the South Pole