First-order benchmark - Ittosuijyunten

...Therefore, the elevation of a point is defined as the distance from that point to the geoid surface measured along a vertical line, and is specifically determined in accordance with the Japanese Geodetic Datum, and is the height when 24.4140 m below the Japanese Geodetic Datum is considered to be 0.0000 m above sea level. After the Japanese Geodetic Datum was established, precise leveling surveys (first-order leveling surveys) were carried out along major roads, and first-order leveling points, which are permanent markers of elevation, were established approximately every 2 km (approximately 17,700 points as of 1982). The routes connecting the first-order leveling points are called first-order leveling routes.

*Some of the terminology explanations that mention "first-order benchmarks" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…したがって，ある点の標高とは，その点から鉛直線にそって測ったジオイド面までの距離と定義されるが，具体的には日本水準原点に準拠して定められるもので，日本水準原点下24.4140mを標高0.0000mとしたときの高さである。日本水準原点設置後，主要道路に沿って精密な水準測量(一等水準測量)が実施され，約2kmごとに標高の永久標識である一等水準点(1982年現在約1万7700点)が設けられた。一等水準点をつなぐ経路を一等水準路線という。…

※「一等水準点」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報