Historical Review of Land Survey Benchmarks Placed by the Japanese Ministry of Interior in the 1870s

In the 1870s, the Japanese government started a nationwide land survey under the guidance of engineers from the United Kingdom. For the leveling survey, engraved cut-marks (kigou in Japanese) were placed on the vertical surfaces of benchmarks. These benchmarks for measuring the height above sea level were used for topological maps as well as for the construction and maintenance of infrastructure such as roads or waterworks. The early large-scale leveling survey was carried out around 1876 in the Tokyo metropolitan area and along the leveling line of 387km between Tokyo and Shiogama to determine the elevation of the baseline in Nasu, which was used for the first wide-area triangulation survey in Japan. The nationwide land survey project was conducted mainly by the Japanese Ministry of Interior for only about 10 years in the 1870s, after which the Land Survey Division of the Imperial Army took over. Afterward, the cut-marks for leveling were no longer used and replaced with another type that had a projection on the upper surface of marker stones. However, cut-marks can still be seen at about 154 points among the 340 originally placed in Tokyo, Tohoku, and other sites. Although some benchmarks with small cut-marks were placed up until 1930s on large riverbanks or in local districts, those cut-marks were only symbolic signs of the survey and not used as actual markers for measurement.In the UK, the author visited about 50 sites of benchmarks with cut-marks, confirmed that they were the origin of early Japanese benchmarks, and found that cut-marks had more varied forms there than in Japan, including cut-marks with bolts, cancellation signs, engraved on the horizontal surface of structures without horizontal bars, and flush bracket types. These types of benchmark were still in use until recently.In an overview of these benchmarks through the study of historical documentation and original benchmarks in the field in both Japan and the UK, this paper describes the technical transfer of leveling from the UK to Japan. The author hopes that these benchmarks will be conserved as historical monuments, although they have been disappearing in urban reconstruction projects in recent years.