The Prime Meridian runs through Greenwich, England and is at 0° longitude.
For many years, different countries measured longitude from different meridians. The French and Algerians, for example, used the Paris Meridian; the Swedes measured from one that passed through Stockholm. By the 1880s, many people could see the advantages of measuring from a single meridian.
The International Meridian Conference took place in October 1884 in Washington DC. Twenty-five nations were represented at the conference by 41 delegates. The Greenwich Meridian was chosen to become the Prime Meridian of the World. There were several reasons for this; the main one being that nearly two thirds of the World's ships were already using charts based on it.
The voting was 22:1 in favour of Greenwich (San Domingo, now the Dominican Republic, voted against); France and Brazil abstained. The French did not adopt the Greenwich meridian until 1911.
From Pole to Pole, the Prime Meridian covers a distance of 20,000 km.
In the Northern Hemisphere, the Prime Meridian passes through the UK, France and Spain in Europe and Algeria, Mali, Burkina, Faso, Tongo and Ghana in Africa.
The only landmass crossed by the Meridian in the Southern Hemisphere is Antarctica.