伊能忠敬的蝦夷地図採用間宮林蔵的資料？

A few weeks ago the Yomiuri News on-line reported the following:

伊能忠敬の蝦夷地図、間宮林蔵のデータで描く？

2014年08月19日 00時05分

　江戸時代後期、伊能忠敬(いのうただたか)（１７４５～１８１８年）が作製した日本全国測量地図の蝦夷地(えぞち)（北海道）全体が、忠敬の弟子で探検家の間宮林蔵（１７８０？～１８４４年）の測量データに基づいて描かれたと考えられると、伊能忠敬研究会が１８日、発表した。

　定説では、忠敬が未測量の北海道北側部分のみを林蔵のデータで補足したとされていた。

　同会は、１８００年の第１次測量で測った函館付近から厚岸(あっけし)付近まで南側の海岸線について忠敬が作った測量図と、１８２１年の最終版「大日本沿海輿地(よち)全図」のデジタル画像を重ね合わせて比較。その結果、両図で海岸線が最大数キロ離れていることを確認した。

　同会によると、忠敬は第１次測量で南側だけを測って以後、蝦夷地を訪れていない。一方、林蔵は蝦夷地を測量したデータを１８１７年に忠敬に引き継いだとされる。忠敬は、弟子以外のデータを用いない方針だったという。同会の渡辺一郎・名誉代表は「最初の測量で自信がなかった第１次のデータでなく、林蔵のデータを用いて正確な地図を作ろうとしたのでは」と話している。

(試譯文)

The Ino Tadataka study group announced on the 18^th (August) that, about the Ezo place (Hokkaido) in the whole Japan national survey map which Ino Tadataka (1745 –1818) produced in the late Edo period, it was thought that the map was drawn based on the survey data by one of Tadataka's pupil explorer Kura Miyabayashi (1780? - 1844)

In the established theory, it was supposed that only the Hokkaido north side portion was not surveyed by Tadataka and was supplemented by the data of Kura Miyabayashi.

The same study group used the image of the survey map on the south coastline from Hakodate to near Akkeshi measured by the first survey in 1800 made by Tadataka, piled up and compared it with the 1821 digital final edition of the "Complete map of great Japan coastal land". The result confirmed that in both maps the coastline had a difference of several kilometers at the maximum.

According to the same study group, Tadataka in the first survey only measured the southern side and thereafter had not visited the Ezo place. On the other hand, the data on Ezo place surveyed by Kura Miyabayashi was taken over by Tadataka in 1817. Tadataka had said that he did not plan to use any data other than his pupil. Ichiro Watanabe, the honorable representative of the study group said "rather than using the data of the first survey which had no confidence, the data of Kura Miyabayashi was used to make an accurate map".

It is an interesting historical discovery. These maps were of top quality in those days.