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You lost me there with the 6 million X coordinates in California. 6 million whats starting from where? It can't be feet from the prime meridian, that's not far enough.

I've been scraping my county assessor's GIS database for property outlines and I noticed that the coordinates are huge, as you mentioned. I assumed it was just some fanciful origin but I'd love to know the story.

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Yeah, it's feet measured east and north of an arbitrary point southwest of everything in the state. There is an actual point inside the state used as a base but they set up a false easting and false northing by subtracting a large round number such that the origin of the coordinate system is southwest of everything in the state. A lot of things in surveying are designed such that the math is easier for people working in the field to reliably get correct.

Probably a https://en.wikipedia.org/wiki/State_Plane_Coordinate_System zone.

Typically designed to have similar error across the whole area and things like that.

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