Australia sits atop one of the fastest-moving tectonic plates in the world. We move about seven centimetres north-east every year.
“That’s about the speed your hair or fingernails grow,” says NSW Surveyor General Narelle Underwood, who led NSW’s ‘jump’.
In the days of paper maps our tectonic drift did not pose a real problem. The continent might move but the distance from Melbourne to Sydney stayed the same. That meant Australia could get away with the slight inaccuracy that has crept in since we last set our coordinates in 1994.
But paper maps have gone the way of the dinosaurs; we use GPS now. And GPS notices.
That’s because GPS satellites precisely locate you on the surface of the Earth.
Because Australia’s underlying map data is now off by about 1.8 metres, it throws off the accuracy of the GPS location. The blue dot is accurate, but the underlying map is not.
“Effectively the coordinate you have from your GPS has already moved the 1.8 metres – it’s the mapping data that has been left behind,” says Dr John Dawson, director of positioning at Geoscience Australia, the federal government department supervising the fix.
Add in the inaccuracy of GPS itself – it is accurate to about five metres – and that explains why you can sometimes open Google Maps and discover yourself trapped inside a building or drowning in a lake.
To fix this, all Australian states and territories have agreed to update their coordinates by June. However, they are all doing it at their own speeds.
On January 1, the Victorian and NSW governments updated the coordinates of every road, property and geographical feature in their states, essentially moving the south-eastern seaboard 1.8 metres north-east overnight.
Official government road maps and property boundaries will now line up perfectly with GPS location data.
“The real importance with data is it all lines up. Roads, people’s property boundaries all line up,” says Ms Underwood.
It will take some time for companies like Google to pick up and implement the new data. But when they do, you will enjoy slightly more accurate satellite navigation.
Towards pinpoint accuracy
The coordinate shift is part of a wider project: super-accurate GPS.
The federal government has invested $225 million to upgrade Australia’s GPS accuracy to a resolution of just 10 centimetres.
To do that, Geoscience Australia is busy building GPS stations across Australia, and has plans to launch two new satellites into orbit over the continent – the necessary infrastructure to calculate position down to a centimetre.
The project is handy for the average person, but its real value is in the future. Driverless cars, for example, need precise GPS data to know which lane they are in, and driverless tractors need to be able to get right up to the fenceline without ploughing it down.
Liam is The Age and Sydney Morning Herald’s science reporter