The “Sokuchi-Genzu” owned by the General Library of the University of Tokyo is the “Shita-zu”, which are namely the manuscripts of the first real surveyed maps by Inoh Tadataka(1745-1818). It is composed of 93 sheets which are 1 large scale(1:36000), 36 medium scale (1:216000) and 56 small scale(1:432000).
On the each Sokuchi-Genzu, the surveyed points are plotted by pin holes and the surveyed lines are drawn by tying them. Furthermore, the place names and the astronomical observed points are recorded. On the medium scale Sokuchi-Genzu, the survey results during several days are plotted and the distances of directions of south-north and east-west between the end points of each survey line were measured on the correspondent large scale map mapsheet and were scaled down one sixth. The drawn areas on some of medium scale Sokuchi-Genzu corespond to the contents of some of Shita-zu owned by Inoh Tadataka Memorial Museum, which are the manuscripts of the Large scale maps.
On the other hand, the map sheet line of directions of south-north and east-west are drawn on the small scale Sokuchi-Genzu. These lines coincide with the map frameworks of the Large scale maps. The length of each framework lines and the distances between the cross points of each survey line and framework lines were scaled down one twelfth by using the reduce measure from the large scale map sheets.
These distances recorded on both scale SokuchiGenzu are expressed by the Japnese measuring system, namely “Shaku-Sun-Bu-Rin”=“30.3cm-3.03cm-3.03mm-0.303mm”. The numerical values under Rin are described by the multiple figures of 1/12. These were read by using the reduce measure on the large scale．
Since Ohtani Ryokichi's voluminous “INOH Tadataka” (1917), it has been commonly accepted that the small scale map were reduced from the medium scale map by reduction in half. However, as the framework of small scale Sokuchi-Genzu corresponds to that of the large scale map, it is said that the small scale maps were prepared from the
large scale mapsby scaling down one twelfth.. The medium scale maps were prepared by reduction from also the large scale maps, so that the medium scale maps and the small scale maps were prepared separately.
