Geodetic Datum Origin of Japan

Central reference point for all Japanese surveys

First up this sightseeing locale is only really recommended for mapping diehards. To give some perspective the place doesn’t even make TripAdvisor’s list of 623 ‘things to do’ in the Minato ward – heaven forbid Tokyo. So, with that out the way, let’s take a look at the origin of longitude and latitude in Japan or the Nihon Keiido Genten.

Tucked away in a tiny park at the end of a cul-de-sac near the Russian Embassy and next to the Tokyo American Club finds a plaque dedicated to Japan’s Geodetic Datum (a fancy name for the coordinate systems used in mapping the earth). Originally the Tokyo Astronomical Observatory stood at this very site with a coordinate baseplate positioned at the centre of a meridian circle (an instrument for timing of the passage of stars). The 1923 Great Kanto earthquake caused the meridian circle to collapse though a metal marker was reestablish in the same spot.

So why is this measurement important? Well, apart from serving as a foundation for the country’s longitude and latitude it acts as a central reference point for public and basic surveys. If you’re passing through the area and mildly interested in mapping history it could be worth a look-see.

Japanese origin of longitude and latitude, Minato-ku, Tokyo.

Nihon Keiido Genten showing reference plate (right).

Official Japanese longitude and latitude origin.

The cardinal points.