Australia has recently announced a 1.8m shift in its mapping coordinates, to compensate for the country’s 7.5cm shift north each year. Inevitably the question is why, and could the same thing happen here?
In Australia, the shift is to take into account the growing difference between maps (and the coordinate reference system they’re based on) and the system used by satellite positioning (GPS). It’s a fact that the world is constantly shifting on tectonic plates, but maps (and their users) like fixed coordinates that don’t change. Before GPS, this was simple to achieve as most positioning and mapping was created from fixed ground points in a coordinate reference system tuned to a particular country. In Great Britain our fixed points included the very familiar trig pillars and we have a mapping coordinate reference system called OSGB36 National Grid which is fitted closely to our little bit of the Earth. Tectonic plate movements had little or no impact on the mapping coordinates or fixed points because they all moved “as one” and generally stayed the same shape.