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).

Zero longitude was first located in the Portuguese Madeira Islands (indicated by the red-and-blue-flag). For the next 300+ years the world calculated longitude from Portuguese islands. Even as their sea-power waned, Portugal's prime meridian remained the world standard until the English achieved dominance during the nineteenth century. As nautical charts increasingly became produced in Greenwich sailors began to use both Porutuguese and English standards. In 1884 a European conference ratified the English placement of the prime meridian in Greenwich. Spanish (red-and-yellow flag) islands lay further east than appears on this map.