The true north and magnetic north are not drawn in the maps of 1:36000 made by INO Tadataka at the beginning of 19th century. In this paper, the author developed method of estimation for the geographic meridian and magnetic meridian for digitized Ino maps. Correlation index between longitudes in the actual digital map of the Geospatial Information Authority of Japan and coordinates in the rotated map image becomes the maximum when the north of rotated map matches to the true north. In this way we were able to fix the north in Ino map of 1:36000.
Ino had believed that the magnetic north was equivalent to true north anywhere through surveying and making maps of Japanese Islands. Therefore, north-south direction in his maps of 1:216000 is magnetic meridian which crosses parallels drawn at right angles. Notwithstanding lack of parallels in the map of 1:36000, we were able to fix the magnetic north comparing with the parallel of the map of 1:216000. This method is the same as true north fixing.
