The Drawing Process of Maps by Inoh Tadataka Studied from His Draft Maps

Abstract

 Inoh Tadataka (1745-1818) drew the first Map of Japan based on a scientific survey. The maps forming Inoh's Map are classified into large-scale map (Daizu 1/36000), medium-scale map (Chuuzu 1/216000), and small-scale map (Shouzu 1/432000). Each map forming Inoh's Map was drawn from manuscript maps called Shita-ezu (1/36000), Yosezu (1/36000), Chuuzu-shitazu (1/216000), and Shouzu-shitazu (1/432000). Shita-ezu is a draft map plotted from the results of a survey carried out over one day. Yosezu is a manuscript map created by combining several Shita-ezu. Chuuzu-shitazu is a manuscript map reduced to one-sixth scale from Yosezu. Shouzu-shitazu is a manuscript map reduced to one twelfth from Daizu, which is compiled from a number of Yosezu. Concerning the mapping process used to draft Inoh's Map, a theory of Ohtani, R. (1917) has been most fundamental and influential in studies of Inoh's Map. According to this theory, Shita-ezu was plotted from the results of a daily survey and Yosezu was compiled from several Shita-ezu. Furthermore, he states that for the Tsukitehon, a Daizu manuscript was compiled from several Yosezu, and then Yosezu were graphically reduced and compiled to create Chuuzu, which in turn was reduced to Shouzu. On the other hand, recently, Nogami, M. (2021, 2022) rejected Ohtani's theory and concluded that Inoh's Map was drawn by calculating the coordinates of survey points, and map reduction was also based on calculations. In this study, it is concluded that the process of drawing Inoh's Map is divided into two flows. One is the reduction process from Yosezu to Chuuzu, the other is the reduction process from Yosezu to Daizu and from Daizu to Shouzu. The terminal survey points on Shita-ezu were plotted by calculating coordinates, which means the east-west/south-north component distance on a map. However, the survey points between the terminal survey points were then plotted graphically on Yosezu. It is added that the plotted areas of each Yosezu and each Chuuzu-shitazu correspond. Therefore, after Yosezu was drawn by combining Shita-ezu, Chuuzu-shitazu were drawn sequentially by reducing Yosezu. Regarding Shouzu-shitazu, it is clarified that the framework of the plotted area of Shouzu-shitazu is the same as that of Daizu. Consequently, Shouzu-shitazu were drawn by reducing to one twelfth the area of the same framework as Daizu after the frameworks of Daizu were decided.