The First Prime Meridian on a Nautical Map

A prime meridian is the place where to start measuring east-west distance. While the equator can only be in one place, the prime meridian can be anywhere you chose.

The first country to create world sailing charts (Portugal) put the starting point in its territory (Madeira Islands-indicated by the red-and-blue-flag).

Close-up of prime meridian , with alternating blue and red colors for individual latitude degrees.

Location of prime meridian on a 1516 nautical chart.

History of Prime Meridians on Sailing Charts: Portuguese map-maker Pedro Reinel drew the first prime meridian (starting point for measuring longitude) on a sailing chart in 1506. While the Portuguese fixed zero longitude at the Madeira Islands for their overseas voyages, their competitors, the Spaniards, soon chose nearby Ferro (Hierro) in their territories (Canary Islands) for their zero longitude. (shown with red-and-yellow flag on map at left. By the nineteenth century, when the English achieved dominance at sea, they began producing charts using their own island for zero longitude. In 1884 a conference held in Washington, D.C. ratified the placement of the prime meridian in Greenwich England. While the most common prime meridian, to this day, more than a dozen countries do NOT use the Greenwich meridian (for their maps) including Austria, Norway, Switzerland, and Indonesia. *While waiting to someone to invent a sufficiently accurate clock, the Portuguese devised a series of highly accurate approximations including the lunar distance model and the path of the solar eclipse.