5 Possible centre points of Australia
Centre of gravity method Over time and with ingenuity, several other methods for calculating the possible centre of mainland Australia have been developed. Covered in more detail below, the results enclose an area which includes the town of Alice Springs and the MacDonnell Ranges, two icons of central Australia.
For the states and territories, we have used a simple conical projection, and reprojected the coordinates using the Australian Geodetic Datum (AGD66) and ArcInfo Software by ESRI. The results are compatible with most paper maps currently in use, but are based only on the mainland areas of each State and Territory. (Islands and batteries not included!)
1. Centre of gravity method
More than 50,000 digitised points representing the coastline of mainland Australia were assigned a unit weight. The moments were calculated assuming equal units of latitude and longitude, the latter varying with the cosine of latitude. So what does all this mean? Imagine you had a perfect cut-out of Australia, with thousands of tiny weights distributed along the perimeter. The centre would be the place where you could balance the cut-out on a pin, and it would be perfectly horizontal. The results for this method would be:
23° 07' 00" South, 132° 08' 00" East; position on SF53-13 Hermannsburg 1:250 000 and 5351 Glen Helen 1:100 000 scale maps.
2. Lambert gravitational centre
In 1988 the Royal Geographical Society of Australasia determined, as a Bicentennial project, the geographical centre of Australia. A monument was erected to mark the location and named in honour of Dr. Bruce P Lambert, a former Director of the Division of National Mapping, for his achievements in the national survey, levelling and mapping of the continent. Similar to the centre of gravity method, the location was calculated from 24 500 points at the high water mark of Australia's coastline.
In the 1930s when Dr C.T. Madigan travelled through Central Australia he calculated the centre of gravity by using a metal cut-out of Australia with a plumb bob and string. His crude measurement was surprisingly accurate as he selected a point less than 11 kilometres due west of this present position.
The computed result of the 1988 project was:
25° 36' 36.4" South, 134° 21' 17.3" East; position on SG53-06 Finke 1:250 000 and 5746 Beddome 1:100 000 scale maps.
3. Furthest point from the coastline
A series of concentric circles drawn on transparent material were moved over the top of a 1:5 million scale map of Australia until one circle was found to touch the coast at three points. Think of it as the largest perfect circle that could be drawn anywhere inside Australia that only just touches the coastlines. The centre of the circle was then marked and the coordinates scaled from the map. This method resulted in a good agreement with the centre of gravity procedure. This is remarkable, and due to Australia's shape rather than any general rule of correlation between the two methods.
23° 02' 00" South, 132° 10' 00" East; position on SF53-13 Hermannsburg 1:250 000 and 5351 Glen Helen 1:100 000 scale maps.
4. Median point
The median point was calculated as the midpoint between the extremes of latitude and longitude of the continent. Basically what this means is that a box was drawn around Australia, just touching the northern, eastern, southern, and western-most points on the continent . Lines were then drawn from the diagonals, with the intersection giving the following coordinates below. What's interesting though is this; both this method and the furthest point from the coastline method produce coordinates that are within the ball-park of the other weighted methods. That means that despite the irregular coastline, Australia's distinctive shape actually has a relatively high degree of symmetry.
24° 15' 00" South, 133° 25' 00" East; position on SG53-01 Henbury 1:250 000 and 5549 James 1:100 000 scale maps.
5. Johnston Geodetic Station
This trigonometric survey cairn, situated about one kilometre north of Mt Cavenagh Homestead, was built by officers of the Division of National Mapping in 1965, and was once the central reference point for all Australian surveys. It was named after Fredrick Marshall Johnston, former Commonwealth Surveyor General and the first Director of National Mapping. Today, surveys are based on the Geocentric Datum of Australia (GDA), a new and more accurate Australian coordinate system which has replaced the Australian Geodetic Datum (AGD) of which the Johnston station is a major part. Further information on datum types and their applications is available from the geodesy pages, or from the Inter-governmental Committee on Surveying & Mapping (ICSM).
25° 56' 49.3" South, 133° 12' 34.7" East; position on SG53-05 Kulgera 1:250 000 and 5546 Kulgera 1:100 000 scale maps.
ref: http://www.ga.gov.au/scientific-topics/ ... #heading-2
