What is the first grid system used in the Philippines?

The World Polyconic Grid was indeed the first grid system used in the Philippines. This system was developed originally for use in mapping and surveying, providing a way to represent the curved surface of the Earth on flat maps. The Polyconic projection is particularly useful for local mapping purposes, as it maintains the accuracy of area, shape, and distances within limited regions, making it suitable for the diverse topography and geography of the Philippines.

While the other systems mentioned, such as Vigan Datum and Philippine Transverse Mercator, were developed or used later, they are part of subsequent advancements in geodetic practices that improved upon the foundational frameworks established by earlier systems like the World Polyconic Grid. The Mercator Grid System is more commonly associated with marine navigation than with terrestrial surveying and mapping in the context of the Philippines, which further emphasizes the significance of the World Polyconic Grid as the pioneering grid framework in the country’s geodetic history.