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Why Japan's Coordinate System Is Uniquely Complex
Japan has three active datum layers: the legacy Tokyo Datum (EPSG:4301), the 2000-era JGD2000 (EPSG:4612), and the current JGD2011 (EPSG:6668). The Tokyo Datum's shift from modern geocentric systems is massive —typically 450 to 700 metres depending on region. Even using JGD2000 data in Tohoku after 2011 without applying the coseismic correction can introduce errors of 0.5 to 1 metre.
GSI mandates use of the official grid files tky2jgd.gsb and touhokutaiheiyouoki2011.gsb via EPSG operation 6714 for professional surveying work. Any simplified Helmert approximation introduces residuals of 10—0m, unacceptable for cadastral or infrastructure applications.
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The $50,000 Geodetic Drift Liability: NAD83 vs WGS84
Because the North American Plate moves ~2cm/year, NAD83(2011) and WGS84(G1762) currently diverge by over 2.2 meters. Using a "standard" GPS WGS84 coordinate for a high-precision NAD83 cadastral staking has triggered $50,000 Professional Liability claims for foundational rework and utility misplacement.