Tokyo Datum (Tokyo 1918 | EPSG:4301)

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Introduction

Tokyo Datum (Tokyo 1918 | EPSG:4301) is a geodetic reference frame adopted by Japan in the early days. Its ellipsoidal parameters (such as the major semi-axis and inverse flattening) are set based on old surveying techniques, and the prime meridian passes through the original site of the Tokyo Observatory (not Greenwich). This coordinate system is mainly used for mapping and engineering surveying in Japan. After its establishment in 1918, it has long served the Japanese geographic information field. However, due to technical limitations, its accuracy and compatibility with international standards have gradually fallen behind.

Coordinate System Composition

Tokyo Datum (Tokyo 1918 | EPSG:4301) belongs to the local area coordinate system. Its coordinate structure is composed of ellipsoid parameters, origin, orientation and scale factor as the core, as follows:

Ellipsoid parameters: This coordinate system uses the Bessel 1841 ellipsoid with a major semi-axis of 6377397.155 meters and an oblateness of 1:299.1528. These parameters define the shape and size of the earth’s ellipsoid and are the basis for coordinate calculations.
Origin: The origin of the coordinate system is set in Japan and is usually associated with a geographically significant location to locate the reference point of the coordinate system.
Orientation: The direction of the main axis of the coordinate system follows a specific geographical orientation, ensuring the directional consistency of the coordinate system in space.
Scale factor: This coordinate system uses a specific scale factor to ensure the accuracy of measurements and correct deformation caused by the difference between the shape of the ellipsoid and the actual shape of the earth.

Pros

**Local adaptability: **The Tokyo 1918 coordinate system was designed specifically for Japan’s geographical features. Under the measurement conditions at the time, it could better meet the map drawing and engineering measurement needs of Japan.

Cons

**Limited accuracy: **Limited by the surveying technology and equipment of 1918, the accuracy of this coordinate system is relatively low and cannot meet the needs of modern high-precision geolocation.
**Incompatible with international standards: **The Tokyo 1918 coordinate system is different from the internationally widely adopted coordinate systems (such as WGS84), resulting in complex coordinate conversions in cross-border or cross-regional geographic information applications.
Outdated technology: With the advancement of surveying technology and the development of geographic information science, the Tokyo 1918 coordinate system has gradually been replaced by more accurate and more universal coordinate systems.

Application Scenario

Tokyo Datum (Tokyo 1918 | EPSG:4301) is mainly suitable for mapping, engineering surveying and land management scenarios in Japan in historical periods. It meets the basic geographic information needs in the absence of modern high-precision technology. However, due to its limited accuracy and incompatibility with international standards, it is currently not suitable for modern application scenarios that require cross-border collaboration, high-precision positioning or integration with global geographic information systems.

Example

GDA2020.