Origin of the First Latitude Scale and First Prime Meridian (Longitude)

Portuguese map-maker Pedro Reinel first drew latitude scale on the prime meridian (starting point for measuring longitude) in 1506. By the 1520s Portuguese experts realized that the scientific precision equal to that they had achieved in fixing latitude could only be approximated in establishing longitude. Only a sufficiently accurate clock would finally solve the problem, they said. Until such a time, they suggested a variety of ways of estimating the difference in time between the starting point (prime meridian) and where they were, including the path of the solar eclipse.

Latitude scale on a 1516 nautical chart, drawn, as was the custom, on the prime meridian (starting point for measuring longitude).

The Portuguese fixed zero longitude at the Madeira Islands (indicated by the red-and-blue-flag) and used this place for all their overseas voyages. But as the secret of navigating the South Atlantic spread, many powers used the Portuguese starting point, while others started to use their territories for zero longitude. Portugal's rival Spain (red-and-yellow flag), set zero longitude in their possession the Canary Islands. 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.