On 09/06/2026 16:01, Graham Whaley wrote:
The OS trig data says (iirc) that it should still be accurate to 0.1m
It shouldn't be! Continental drift should have changed it by almost double that. Even the longitude of Greenwich varies relative to WGS 84, over time, and latitude also does. GPS uses the WGS 84 reference frame, not the ETSR89 one, which is specific to the Eurasian tectonic plate, so is gives more stable coordinates in past and present parts of Europe.
The national grid references should be stable, but OSM is GPS based, not NGR based.
(It is possible that some high precision GPS receivers return coordinates that are corrected for this, but I don't think those are true GPS coordinates.)
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