Surveying Method and Mapmaking Techniques of INO Tadataka

Abstract

Around 200 years ago, INO Tadataka surveyed and mapped almost all coastlines and main roads in the Japanese islands as polygonal lines of traverse courses. He wrote booklets in which the coordinate values of the nodal points were described, and derived the coordinate north-south values (equivalent to latitude) from a surface survey using dosen-ho (a type of open-traverse method). INO also corrected values based on astronomical observations carried out at 1,220 sites, for which he used the method of letting A equal the north-south coordinates obtained by surface survey and B equal those obtained by astronomical observation, after which the correction factor was expressed as (A-B)/A. Because chronometers were not available, INO was not able to correct the east-west coordinates obtained from the surface survey directly. Therefore he adopted the same correction factor in all probable east-west coordinates. He drew maps on the scale of 1/36,000 and 1/216,000 by plotting the above-mentioned coordinates on the maps in a rectangular system. In the maps scaled at 1/216,000, he showed latitude as straight lines at even intervals and longitude as polygonally approximated lines after the Sanson-Flamsteed method. The equidistant projection on the rectangular coordinate system was within the permissible range in 1/36,000 maps but was not a well-chosen projection method in 1/216,000 maps.