Japan Horizontal Datum

 This page explains "Japan Horizontal Datum", or "Japan Geodetic Datum" and I quoted an inferior web site and wikipedia.

 It is the datum point to decide latitudes and longitudes. 
 There was once an astronomical telescope called "Meridian Circle". It was built in 1892 and smashed by the "Great Kanto Earthquake of 1923". Now, only the foundation remains (Look at inferior photos).

The central point between 2 black marble stones is
the "Japan Horizontal Datum".

 The point is located at Long.１３９°４４′２８″.８８６'E and Lat.３５°３９′２９″.１５７２'N. These numbers were measured by using most advanced technology on October 21, 2011




↓ Here is an explanation written in Japanese by the Geographical Survey Institute.
http://www.gsi.go.jp/kanto/ki8cgenten.html