Difference Between Tokyo Datum and JGD2011

Examine the 400+ meter shift from the legacy Tokyo Datum to ITRF-aligned JGD2011, handling post-earthquake coordinate adjustments in Japan.

JGD2011 (EPSG:6668)
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Magnitude: 400+ meters
Tokyo Datum (EPSG:4301)

1. The Massive Local to Global Shift

Historical map data in Japan was defined using the Tokyo Datum (Bessel 1841 ellipsoid). When GPS was widely adopted, a massive discrepancy emerged: raw WGS84/ITRF coordinates varied from Tokyo Datum coordinates by over 400 meters depending on the region.

⚠️ Warning: Raw GPS to CAD Coordinate Discrepancy

Combining uncorrected WGS84 drone data with NAD83 site plans creates a structural shift of 1-2 meters. Review the massive legal implications of this error.

Explore Boundary Dispute Liability →

2. The Evolution: JGD2000 and JGD2011

To align with global satellite systems, Japan shifted entirely to the Japanese Geodetic Datum 2000 (JGD2000), which tied directly into the ITRF. However, following the catastrophic 2011 Tohoku earthquake, portions of eastern Japan shifted physically by several meters. The Geospatial Information Authority of Japan (GSI) released JGD2011 to account for this violent tectonic deformation.

Tectonic Compliance: JGD2000 and JGD2011 utilize identical geographic definitions in regions unaffected by the quake. However, in deformed regions, failing to use the official GSI parameter adjustments (jgdtrans grid files) will embed meters of error directly into engineering plans and property lines.

3. Transformation via GSI Grids

Transforming coordinate data from Tokyo Datum to JGD2011 requires the use of regional grid parameter files provided by GSI.

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Professional Risk Notice

Using the wrong datum or applying coordinates without grid-to-ground correction can cause 1–400 metre positional errors — a leading cause of surveying negligence claims and contract disputes.

📋 See Legal Cases ($25K–$10M) → 📝 Contract Datum Risk → ⚙️ Calculate My Exposure →
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