Photo/IllutrationLife-size reproductions of Ino Tadataka’s map assembled in a sports gym in Katori, Chiba Prefecture. The map was so big that the island of Hokkaido had to be placed southwest of its actual position. (Yoshito Watari)

  • Photo/Illustraion
  • Photo/Illustraion
  • Photo/Illustraion
  • Photo/Illustraion

Even 200 years after his death, the mystery has deepened over Ino Tadataka’s map of Japan, a work so accurate that the Tokugawa Shogunate considered it a matter of national secrecy.

The map was created at time of national isolation and increasing traffic of European ships in Asia. Even officials of various domains in Japan during the Edo Period (1603-1867) were said to be forbidden from receiving details of the map.

However, recent findings indicate that the map was not so secret after all.

The incredible effort of Ino (1745-1818) in mapping Japan is no mystery. He walked for about 40,000 kilometers along the Japanese coasts over the first two decades of 19th century.

Ino was a businessman, a self-taught scholar, surveyor and one of the most illustrious non-samurai figures of the era.

He headed a tradesman family and lived in today’s Katori, Chiba Prefecture. After his retirement, he moved to the capital Edo, today’s Tokyo, at the age of 50 to study under Takahashi Yoshitoki, a governmental astronomer, calendar maker and surveyor.

Governmental astronomers were also in charge of translating European scientific publications and studying their contents.

Ino initially took up surveying to work out the length of one degree latitude on the ground, a problem that had perplexed Japanese astronomers, and to accurately calculate the circumference of the Earth.

From 1800, at 55, he walked the coasts and main roads of all corners of Japan, except the Okinawa islands, on 10 survey trips over 17 years. The goal was to create an accurate cartographic map of the nation.

From his fifth trip, it became a national project, directly sponsored by the Tokugawa Shogunate.

At that time, maps commonly available in society were more like pictorial charts illustrating geographical features or landmarks, depending of their purposes. They showed little regard for accuracy in sizes or shapes.

Ino’s work changed all that.

Three years after Ino’s death, copies of complete maps, titled “Dai Nihon Enkai Yochi Zenzu” (Maps of Japanese coastal areas), were made in three sizes in 1821.

The largest map, made in the scale of 1:36,000, consists of 214 separate sheets. When assembled flat, the map is 47 meters long and 45 meters wide.

The midsized map was made at a scale of 1:216,000 and consists of eight sheets.

The smallest one, made up of three sheets, is in the scale of 1:432,000.

“The purpose of (the largest map) is to establish the geographical shape of Japan, and it was not made for practical use,” said Masateru Yamaguchi, a curator of the city-run Inoh Tadataka Museum in Katori. “I imagine the midsized and small maps were produced in sizes that would still retain the necessary information, as the largest map was too big for anyone to use.”

Legend has it that sailors of the British fleet that came to Japan at the end of Edo Period were surprised by the quality of Ino’s map.

It is almost as accurate as today’s maps, but experts have pointed out that Hokkaido and the Tohoku region on Ino’s map are stretched to east, while southern Kyushu protrudes to east slightly.

According to Takehide Hishiyama, director of the Ino Tadataka Society, latitude was relatively easy to work out by observing the stars. To determine longitude, the time difference must be calculated between two points. Making matters more difficult was the fact that there were no accurate clocks in Japan in the early 19th century.

Ino is believed to have drawn imaginary longitudinal lines on his map based on mathematical calculations.

However, Hishiyama says the difference is negligible if longitudes are ignored.

“The accuracy of Ino’s map is not bad at all,” Hishiyama said. “I think he made a deliberate decision to keep the contours of the land and to believe in the results of his faithful survey after mulling over the technical problem of rendering round Earth onto flat paper.”

The Tokugawa Shogunate was long believed to have strictly controlled Ino’s map as a highly sensitive document.

In 1828, Phillip von Siebold, a German doctor and scholar staying in Nagasaki, was caught attempting to take a copy of the map home. He was deported in this “Siebold Incident,” and people involved in the plot were punished, including Takahashi’s son, Kageyasu.

But recent studies show the map may not have been such a well-kept secret.

In April this year, the Hiroshima Prefectural Museum of History said it found a replica of a map of the eastern half of Japan that was produced by Ino after his fourth survey trip. It was discovered in a pile of donated items.

The map was copied by Suzuki Kansei, a civilian scholar, in 1807, only three years after Ino submitted the original to the government.

Suzuki was a former “churo,” or assistant to a minister, of the Takada Domain in today’s Joetsu of Niigata Prefecture, but he had fallen from power.

Sections of Japan were plotted after each survey trip before the complete map was produced in 1821.

“It is likely that the partially finished maps circulated among public intellectuals who were interested in the international situation,” Minoru Kuge, the chief curator of the Hiroshima museum, said.

Other historical sources have said Ino’s survey team was prohibited from sharing details with officials of domains that they were walking through.

However, Junko Suzuki, the representative director of the Ino Tadataka Society, said such descriptions may have been altered in later years.

According to Suzuki, an uncolored replica of the final edition of Ino’s map was passed down to the offspring of Ishiguro Nobuyoshi, a village chief in today’s Imizu, Toyama Prefecture. Nobuyoshi was also a surveyor who had once met with Ino.

“The impact of the Siebold Incident may have contributed to the overly emphasized idea of ‘secret,’” Suzuki said.