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Chuo-ku Tourism Association Official Blog

Chuo-ku Tourism Association correspondent blog

Introducing Chuo-ku's seasonal information by sightseeing volunteer members who passed the Chuo-ku Tourism Association's Chuo-ku Tourism Certification and registered as correspondents.

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The height of Mount Fuji is also from here, Reiganjima Water Observatory

[The cat on the slope] January 31, 2011 11:10

What is the highest mountain in Japan?

Yes, it's Mount Fuji.

So what's the height?

You all know this, 3776m. I remember, "Everyone (3776)."

By the way, the height of the Sky Tree is said to be Musashi (634m).

So, where is the height of Mount Fuji based on?

Yes, that's right. It is the "Japan Standard" located in 1-1 Nagata-cho, Chiyoda-ku.

Finally, one more thing. When and where did the Japanese standard be established?

You may not know this unless you have a little bit of a traffic.

The answer was "Meiji 24 (1891), based on the Reiganjima Water Level Observatory."


That's why today's theme is Reiganjima Water Level Observatory.

In 1873, water level station was established on Reigan Island as one of the water markers for measuring the estuary water levels of major rivers. Then, for the six years until Meiji 12 (1879), except for a four-month absence, we observe the water levels at high tide and low tide here every day, and based on the data, the average sea level of Tokyo Bay, that is, nationwide We have set the height standards.


After that, in 1891, when setting up a Japanese benchmark in Nagata-cho, Chiyoda-ku, the level was measured from the Reiganjima Water Level Observatory to the origin, and the height of 24.5000m was used as the reference point (Note 1).

The Reiganjima Water Level Observatory can be said to be the cornerstone of modern surveying in Japan.


The Reiganjima Water Level Observatory is still used to observe basic data such as construction plans (Note 2). In addition, due to the revetment work on the Sumida River Terrace, it was relocated 36m downstream from its original location in 1994.

From Chuo-ohashi Bridge. jpg

The current Reiganjima Water Level Observatory, taken from Chuo-ohashi Bridge

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The observation room is designed so that when you move the viewpoint along the river, the shape of the square, the hexagon, and the octagon will change.


(Note 1) It was revised to 24.4140m in 1928 due to the plate tectonic caused by the Great Kanto Earthquake.

(Note 2) Since the reclaimed land in Tokyo Bay has made the Reiganjima Observatory no longer an ideal location for verifying the baseline, we are currently verifying the baseline at the oil pot observatory in Misaki, Kanagawa Prefecture.

For a detailed history of Japan's benchmark and Reiganjima Water Level Observatory, please refer to the local information board ↓ and the Geographical Survey Institute website of the Ministry of Land, Infrastructure, Transport and Tourism (you can enlarge it by clicking the photo).

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Well, what is the water level today?

Also, slightly upstream from the Reiganjima Water Level Observatory, up the stairs connecting Chuo-ohashi Bridge and the Sumida River Terrace, there is a "first-class benchmark / intersection".

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It is well-known that the original road vote, which is the starting point of the Japanese road network, is located in Nihonbashi.

The "starting point" of the height of mountains and land nationwide was also here in Chuo-ku.