伊能図の意義と特色

-伊能忠敬150年祭記念講演 (1968年5月25日東京地学協会総会講演)-

抄録

The name of Tadataka INÔ (1745-1818), who carried out the survey of the almost entire islands of Japan and made excellent maps of Japan in the end of Edo period, became popular all over the country since the Tokyo Geographical Society erected a bronze memorial monument in the Shiba Park, Tokyo in 1889, which was re-established in the same site with a newly designed beautiful stone monument in 1965.
INÔ's Map officially presented to the Takugawa Government in 1821 compiled after his death by his pupils consisted of those of three scales : large scale (1 : 36, 000, 214 sheets), middle-scale (1 : 216, 000, 8 sheets) and small-scale (1 : 432, 000, 3 sheets). Despite its excellency, they were stored in the Library of the Tokugawa Government, only a few limited number of people were allowed to see them, and INÔ's Map proved its usefulness since the Meiji Restoration. These maps served as the basis and the most important data to meet the urgent needs of accurate maps, charts and statistical figures of the Japanese Islands.
However, INÔ's Map has an unfortunate history behind it. After it was handed over from the Tokugawa to the Meiji Government, a fire broke out in part of the Imperial Palace in 1873 and destroyed all the maps. INÔ's descendants presented the preserved copies to the Government and they were kept in the Library of the Tokyo Imperial University, while the fire caused by the Kantô Earthquake in 1923 destroyed the Library. In consequence, the number of INÔ's Map which are extant is very small and fragmental today and yet careful studies of these maps, INÔ's books and documents revealed some points which have never been fully appreciated in his achievements, and the followings are the abstracts of these main points.
(1) INO's motive for undertaking the survey of Japan was the determination of the length of one degree of latitude, which he carefully determined as 28.2 ri (110.85 km) with extraordinary accuracy at that time. However, “Map of the Eastern Part of Japan” presented to the Tokuwawa Government in 1804 was so elaborate, so accurate, so detailed and so beautiful and gave even an impression of a work of art that the Government appointed him as an official and ordered him to continue the survey, which he carried out with extraordinary persistence and skill. Fig. 2 shows the distribution of INÔ's routes of survey, which was carefully drawn from the maps of middle-scale and his records and the total distances of surveyed lines amounted to 33, 724 km. In addition he traveled several times between Edo and Kyôto (Tôkaidô) as well as Kyôtô and Shimonoseki (Sanyô-dô), so that the total distances of his travel were more than 40, 000 km, which he accomplished when he was fifty-six to seventy-two years of age.
The mapped areas are strictly restricted to those of the actually surveyed and certainly known. Therefore, many parts far distant from the roads and the coast left unmapped because the surveys were not conducted. These are some of evidences of INÔ's scientific mind underlying his map-drawing.
(2) The Tokugawa Government's needs to the maps were the accurate drawing of configuration of the coastline of the Japanese Islands as well as the detailed distances of important towns along the Tôkai-dô, the Sanyô-dô, and along the northern part of Kyûshû. INÔ's main aims were the determination of latitudes and, if possible the longitudes, of important towns along the most important zone of Japan at that time, that was along the Tôkai-dô and the Sanyô-dô. INÔ's Map met these needs quite well, following basically what is called the method of traverse with great care, and he also adopted astronomical observations.