Unlike latitude , which has the equator as a natural starting position , there is no natural starting position for longitude . Therefore , a reference meridian had to be chosen . It was a popular practice to use a nation 's capital as the starting point , but other locations were also used . While British cartographers had long used the Greenwich meridian in London , other references were used elsewhere , including El Hierro , Rome , Copenhagen , Jerusalem , Saint Petersburg , Pisa , Paris ( see the article '' Paris meridian '' ) , Philadelphia , and Washington D.C . In 1884 the International Meridian Conference adopted the Greenwich meridian as the '' universal Prime Meridian '' or '' zero point of longitude ''
International Meridian Conference
International Meridian Conference
Longitude