Geographers already have a system for recording positions relative to continental plates - in Europe that means ETRS89 [1], North American NAD-83 [2], Australian GDA94 and so on.

Of course, getting all software to support multiple datums might be a complicated matter, as 98% of things like online slippy maps and mobile phone geolocation APIs just use WGS84, the familiar datum used by GPS.

[1] https://en.wikipedia.org/wiki/European_Terrestrial_Reference... [2] https://en.wikipedia.org/wiki/North_American_Datum

(1) By measuring the location of a few designated landmarks, it should be possible to extrapolate tectonic-level shifts to all other points on the same plate pretty accurately.

(2) Changes on a smaller scale, e.g. due to a landslide, are probably less surprising when they cause a change in location codes. On the other hand, there might be some houses on a hill somewhere slowly sliding down, where the system doesn't work.

(I also realized that my previous comment can be read as supporting a flat earth theory, especially the part about the sphere being imaginary. I firmly believe that the earth is a bumpy ellipsoid, though.)

Fully accurately, you'll only be able to get retrospective locations (and probably some interpolation thereof), for pretty much the same reason that I can't actually tell you for sure exactly how many seconds the next decade is going to have. We won't know how many leap seconds it has until it is over, or the standards body commits to including no more. But I can tell you exactly how many seconds there were in 2000-2009 inclusive.