Australia Cruising North At High Speed

I saw at the BBC that Australia is revising is the standard spatial reference used for mapping and navigation. The Geocentric Datum of Australia has been defined by a position on land, from which all other locations are recorded in Australia. This is simple and straightforward—and problematic.

In one of those “wow” realizations that comes from big picture science, we realize that this reference system is fine, as long as you only care about Australia, and not the rest of the planet. And if the Earth were static, then it wouldn’t matter anyway, because where you are in Australia would be where you are.

But, as the story makes clear, Australia is actually cruising North at about 7 cm per year (which is not bad at all for a continent), so all the coordinates recorded in reference to the old standard (set over 100 years ago) are now 1.5 m too far South of their global position.

This discrepancy is beginning to matter because satellite positioning is common, and is measuring global position, not parochial geopolitical references.   For this reason, the standard will be modified to converge on global position measured from space. (Computers win!)

This also made me think about similar reference systems elsewhere. Is everything wonky now? I realized that this depends on how fast the continental plates are moving, which varies. Many places are not drifting very fast, and these places will have less of a problem (and more time to adjust).

On the other hand, there are cases like the West coast of the US where plates are moving rapidly relative to each other, but are stuck in collision. In these cases, Earthquakes result in sudden changes in position, as the plates slip. This is an interesting problem because the politically defined reference point may or may not move, too. E.g., the US reference and most positions are not affected, only areas near the fault.

Of course, GPS navigation (which cares not a whit about human boundaries) will be thrown into disarray after every major quake, and self driving cars will need a software patch ASAP, lest they drive right off a cliff or something.

So Australia is kind a special case. It is a separate land mass, all moving together at high speed, and has a single political authority.

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