An Archive That Measured a Nation
In 1800, a retired merchant in his mid-fifties walked out of Edo bound for Ezo, the northern island we now call Hokkaido. His name was Ino Tadataka, and over the next seventeen years he led ten survey expeditions along the coasts of Japan, producing the first maps to show the country's true shape and its position on the globe.
The Ino Tadataka Related Materials (Ino Tadataka Kankei Shiryo) are what remains of that project: 2,345 items handed down in the Ino family home in Sawara, now part of Katori City, Chiba Prefecture. The collection spans finished maps and working drafts, survey diaries, letters, astronomy texts copied in Tadataka's own hand, and the instruments his teams carried into the field. Designated an Important Cultural Property in 1957, the entire group was raised to National Treasure status on June 29, 2010, in the comparatively rare category of historical materials.
The collection belongs to Katori City and is housed at the Ino Tadataka Memorial Museum, which faces the willow-lined Ono River in Sawara's preserved merchant quarter.
From Sake Brewer to Surveyor
Tadataka came to cartography late. Born in 1745 in Kazusa Province, in present-day Kujukuri on the Chiba coast, he married into the Ino family of Sawara at seventeen and spent more than three decades running the family's sake brewing and rice trading concerns. Only in 1795, having handed the business to his heir, did he move to Edo and enroll as a student of Takahashi Yoshitoki, the shogunate's official astronomer, a man nineteen years his junior.
What began as the study of astronomy and calendrical science grew into a national undertaking. Between 1800 and 1816, Tadataka's teams traced the coastline of the entire archipelago, fixing latitude by celestial observation and measuring distance on the ground, pace by pace and chain by chain. After his death in 1818, his disciples completed the work. In 1821 the finished atlas, the Dai-Nihon Enkai Yochi Zenzu (Complete Map of the Coastal Areas of Great Japan), was presented to the shogunate.
Those presentation copies were later destroyed by fire. The materials the family preserved in Sawara are the most direct surviving record of how Japan's first measured map was actually made.
Why These 2,345 Items Became a National Treasure
The designation recognizes the collection as the only comprehensive archive of a nationwide survey from pre-modern Japan. It falls into five groups: 787 maps and pictorial maps, 569 documents and records, 398 letters, 528 books and manuscripts, and 63 instruments.
Among the maps are 123 finished Ino maps drawn up after the expeditions, including a set of 69 large-scale sheets covering the country east of Owari, compiled from the first four surveys and shown to Shogun Tokugawa Ienari. Beside them survive 399 working drafts, the intermediate sheets on which raw field measurements were converted into cartography. Few map archives anywhere let a viewer follow that process stage by stage, which is precisely what gives this group its standing among scholars.
The books reveal the science behind the walking. Tadataka's manuscript copy of the Rekisho Kosei Kohen, a treatise on calendrical astronomy, and a partly autograph copy of commentary on the writings of the French astronomer Lalande show him absorbing the most current astronomical knowledge then available in Japan under Takahashi's guidance.
The 63 instruments, divided among devices for celestial observation, land measurement, and drafting, form the best-documented set of surveying tools to survive from late Edo Japan with their provenance intact.
Visiting the Ino Tadataka Memorial Museum
The museum stands on the bank of the Ono River, directly across the water from Tadataka's former residence, itself a nationally designated Historic Site where he lived for over thirty years before leaving for Edo. Crossing the small bridge between the two, you cover in a minute the distance between the merchant's life he gave up and the legacy it funded.
Because paper and ink fade under light, the National Treasure items appear in rotating collection exhibitions rather than all at once; by 2026 these displays had passed their 128th installment, so repeat visits keep turning up different maps, letters, and instruments. A display near the entrance alternates an Ino map with a satellite image of Japan, and the closeness of the two outlines, achieved with wooden rods, chains, and the stars, tends to stop first-time visitors in their tracks.
Plan on thirty minutes to an hour inside.
The museum opens from 9:00 a.m. to 4:30 p.m. and closes on Mondays (or the following weekday when Monday is a national holiday) and over the New Year period. Admission is 500 yen for adults, 450 yen for visitors aged 65 and over, and 250 yen for elementary and junior high school students. Photography in the galleries is restricted to a few marked spots, so leave the camera for the streets outside.
Around the Museum: Sawara's Canal District
Sawara grew rich shipping rice, sake, and soy sauce along the Tone River system, and the wealth shows in the rows of plastered storehouses and wooden shopfronts along the Ono River. In 1996 this townscape became the first in the Kanto region to be selected as an Important Preservation District for Groups of Traditional Buildings, and many of the old houses still trade as shops and restaurants run by the same families.
Flat-bottomed sightseeing boats depart from a landing near the museum and glide beneath Jaja Bridge, named for the sound of water spilling from its aqueduct. The Suigo Sawara Dashi Kaikan, a short walk away, exhibits the towering festival floats of the Sawara Grand Festival, inscribed on the UNESCO Intangible Cultural Heritage list among Japan's float festivals; a combined ticket with the museum is available. About ten minutes away by car rises Katori Jingu, one of the most venerable Shinto shrines in eastern Japan, its lacquered main sanctuary rebuilt in 1700 and designated an Important Cultural Property.
From central Tokyo, the trip takes roughly ninety minutes: JR trains run to Sawara Station, a ten-minute walk from the museum, and highway buses serve the town as well. Drivers can use the Sawara-Katori Interchange on the Higashi-Kanto Expressway, about five minutes from the historic district.
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Q&A
- Can I see the actual National Treasure materials, or only replicas?
- Original items are displayed, but in rotation. Conservation rules for paper documents mean only a portion of the 2,345 pieces is shown at any one time, alongside high-quality reproductions that can be examined closely. Check the museum's website for the current collection exhibition before visiting.
- How accurate were Ino's maps, really?
- Strikingly accurate for coastal outlines. The comparison display in the museum sets an Ino map against modern satellite imagery, and the match along most of the coastline is close enough that the differences take effort to find. The maps remained in practical government use into the Meiji era.
- How do I reach the museum without a car?
- Take the JR Narita Line to Sawara Station; the museum is about a ten-minute walk through the historic district. From Tokyo, transfer at Narita, or use a direct highway bus toward Sawara.
- Is photography allowed inside the museum?
- Generally no. Photography is permitted only at specifically marked points, and the museum asks that any images shared online credit the collection. The streets, canal, and Tadataka's former residence outside are free to photograph.
- Is the former Ino residence open to visitors as well?
- Yes. The house where Tadataka lived and worked before moving to Edo stands just across the Ono River from the museum and is preserved as a national Historic Site, so the two are easily combined in a single visit.
Basic Information
| Name | Ino Tadataka Related Materials (Ino Tadataka Kankei Shiryo) |
|---|---|
| Designation | National Treasure (category: historical materials); designated Important Cultural Property on February 19, 1957, and National Treasure on June 29, 2010 |
| Number of Items | 2,345 (maps and pictorial maps 787; documents and records 569; letters 398; books and manuscripts 528; instruments 63) |
| Period | Edo period |
| Owner | Katori City |
| Location | Ino Tadataka Memorial Museum, 1722-1 Sawara-i, Katori City, Chiba Prefecture |
| Hours | 9:00 a.m. to 4:30 p.m. |
| Closed | Mondays (the following weekday when Monday is a national holiday); New Year holidays |
| Admission | Adults 500 yen; seniors 65 and over 450 yen; elementary and junior high students 250 yen |
| Access | 10 minutes on foot from JR Sawara Station; 5 minutes by car from Sawara-Katori IC on the Higashi-Kanto Expressway |
References
- 国指定文化財等データベース「伊能忠敬関係資料」（文化庁）
- https://kunishitei.bunka.go.jp/bsys/maindetails/201/10142
- 伊能忠敬記念館（香取市公式サイト）
- https://www.city.katori.lg.jp/sightseeing/museum/
- 利用案内（伊能忠敬記念館・香取市公式サイト）
- https://www.city.katori.lg.jp/sightseeing/museum/guide.html
Last verified: 2026.06.10