What is the difference between the existing AGD and the new GDA coordinates?
The Australian Geodetic Datum (AGD) was established before satellite techniques were available and was based on a model of the Earth, that is best suited the Australian region at the time. GDA is based on an international mathematical model which ‘best fits’ the shape of the whole earth, with its centre coinciding with the earth’s centre of mass. Coordinates on the earth’s surface change approximately 200 metres in a north easterly direction with the new datum (GDA). The exact change and orientation of the change will vary slightly from area to area.
