Inō Tadataka

Turning a measured route into a map

Measuring roads alone could not establish Japan’s shape. After business and community work in Sawara, Tadataka studied with Takahashi Yoshitoki and connected astronomical observation with ground measurement. Establishing positions on one map grew into nationwide surveys.

Distance alone could not place distant sites consistently on one map. Bearings and distances traced routes, while astronomical observation checked latitude. Comparing route measurements with observations helped adjust accumulated discrepancies. Surveying combined methods rather than relying on walking alone.

Organizing a team and connecting records

Surveying began with Ezo in 1800 and extended along coasts and roads. Team members, local guides and providers of food and lodging supported it. Ezo was inhabited by Ainu communities, not an empty frontier; survey work also belonged to shogunal policy and existing regional societies.

Bearings and distances went into field books for later calculation. Walking, recording and astronomical observation had to agree. Illegible numbers or inconsistent standards would prevent the measured route from being joined.

As surveying expanded, shogunal support increased; most of the project operated as government business. Lodging, food, guides and funds sustained long journeys, connecting Tadataka’s research interests with public organization.

Completion after his death and the maps’ survival

Tadataka died in 1818; pupils and the shogunate’s astronomical office completed Dai Nihon enkai yochi zenzu in 1821. Large, medium and small series served different uses. The large series comprised 214 sheets at 1:36,000, connecting nationwide records in detailed and overview maps.

The maps detail measured coasts and roads, not every inland area at uniform modern precision. Reachable routes and methods affected coverage. Connecting bearings, distances and astronomical observations nevertheless established a different nationwide cartographic basis.

Submitted maps were lost in the palace fire of 1873; household copies at Tokyo Imperial University were destroyed in 1923. Surviving copies and recent color restorations preserve the information through collecting and conservation. The date of the mapped Edo-period information differs from that of surviving paper or later coloring.

Turning points

1. 1745

   Born.

2. 1790s

   Studied astronomy in Edo after retirement.

3. 1800

   Began the Ezo survey.

4. 1818

   Died before the maps were completed.

5. 1821

   His pupils completed the national maps.

Their legacy

The maps combining survey records and observations were completed after his death. Surviving copies and reconstructed maps reflect the later work of compilation and preservation as well as measurement.