Ino Tadataka’s Survey: Turning Travel into Lines on a Map

Tadataka had not spent his entire adult life surveying the country. In Sawara he worked in the family business and held village responsibilities, including service as a village head.

After transferring household responsibilities, he went to Edo in 1795. There he became a pupil of Takahashi Yoshitoki, an official associated with the shogunate’s astronomical work.

Study of celestial movements and calendars connected with measurement on land. Observation could help establish position, to be compared with distances measured on the ground. His earlier commercial life and later period of study both preceded the national surveys rather than being erased by them.

A coast is not one straight line. Successive points were established, and the distance and bearing from one to the next were measured. This is the basic idea of a traverse.

Imagine proceeding east, then northeast, then changing direction again. Length and direction together allow the route’s bends to be transferred to paper.

Those directions are an explanatory example, not measurements from a particular historical coastline. The principle is that a sequence of short measured lines can describe a larger outline. The generated image does not reproduce an Ino map or a set of authentic survey values.

A length measured along sloping ground is not automatically the distance required on a flat map. The corresponding horizontal distance must be distinguished from the line following the incline.

The National Diet Library explains that gradients were measured and trigonometric tables used to convert distances for the mapping work. Measurement was followed by calculation.

No invented values or claimed error rate for a particular station are supplied here. The point is the procedure: recorded numbers were transformed into quantities appropriate for the map. Simply accumulating ground lengths would miss that computational stage.

The end of daytime measurement did not end the observational work. At night, stellar altitudes were observed using a quadrant. Those observations helped establish latitude.

This supplied a north–south check distinct from the succession of ground segments. Chiba’s explanation of surviving materials includes records of stellar observations as well as directions.

Daytime routes and the night sky thus contributed measurements of different kinds. Combining them required observation and calculation during the journey, not only after returning to an office. The scene remains an anonymous illustration rather than a record of a particular observing night.

Field records gathered distances and directions. Preparing maps required representing the resulting relationships at an appropriate scale. Large, medium and small map series served different levels of detail and geographical overview.

The completed large-scale series used a scale of 1:36,000 and comprised 214 sheets. The medium series had eight sheets and the small series three. These are parts of the compilation, not separate counts of surveying journeys.

The mapped coasts and routes should not be equated with a modern topographic survey of every inland location. Asking what was measured and how it was compiled makes the scope of the achievement more precise without diminishing it.

How did walking become a mapped coastline? The route was divided into short measurable lines, with direction recorded beside distance. Slopes required conversion, and distant features and stars helped check position.

Records then had to be carried forward and compiled at defined scales. The final outline combined field observation, calculation and work shared across several people and years.

The question is therefore not only how far one man walked. It is how successive measurements were checked and made usable. Looking at those procedures reveals the hands measuring on the ground and the eyes observing the sky behind the familiar map.