Tuesday, October 18, 2016

Australia on the Move — Adjusting the Charts to Agree with GPS



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Australia on the Move — Adjusting the Charts to Agree with GPS
// Old Salt Blog - a virtual port of call for all those who love the sea

australia-globeAustralia is, literally, on the move.  A year ago, we posted about how the Prime Meridian, the arbitrary line in Greenwich, UK, marking 0 degrees of longitude, had to be adjusted by slightly over 100 meters after the discrepancy was noted by GPS. While the position of the Prime Meridian marker is interesting and yet of no real practical consequence, on the other side of the world the maps of an entire continent are now continually in need of adjustment. Chances are that any map or chart you may have of Australia has its position at least slightly wrong.

All the world's continent are moving due to plate tectonics, also known as continental drift. The continent also has a slight clockwise rotation. Whereas North America drifts at around one inch per year, Australia is moving at the relatively breakneck speed of 2.7 inches northward per year.

The entire map of Australia has been adjusted four times in the last 50 years. In 1994, the continent was adjusted by a remarkable 656 feet. The next adjustment to be made at the end of this year will be just under 5 feet.

In the days when sextants and chronometers were the most accurate means of determining position, a few feet or even a few hundred feet, wouldn't make much difference. Now, with satellite-based GPS navigators common in most cars, trucks and cell phones, a discrepancy between system maps and the position established by GPS can make a significant difference all across the continent of Australia. Without regular adjustments; roads, harbors, rivers and mountains won't line up with the GPS coordinates.  Whether navigating in narrow channels, routing trucks across the more remote sections of the outback or ordering a pizza delivery in Sydney, a 600 foot plus continental drift is best avoided if possible.

The post Australia on the Move — Adjusting the Charts to Agree with GPS appeared first on Old Salt Blog.


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