2020 Volume 129 Issue 2 Pages 285-301
In 1801, Inoh Tadataka observed the heights of stars at the meridian passage to learn the latitudes of points, and also surveyed surface distances among the points surveyed astronomically. He obtained the distance of one degree as 28.2 Ri under the Japanese system and regarded this value as a definition for surveying and making maps. Therefore, 2538 Ri corresponds to 10000 km in the metric system. Subsequently, he surveyed most of the coastline of Japan and its major roads, and made basic 1:36000-scale maps using this definition. The accuracy of latitudes at astronomical observation points on the 1/216000-scale map is estimated by comparing those on an actual digital map of Japan. The standard deviation of the difference in latitudes between the two maps is within 0.5 minute (0.926 km).