By Historical Consensus the Western Australian Border is not Straight!


The step, dog-leg, or kink in the Western Australia border, where the border between South Australia and the Northern Territory intersects it, is the result of considered and deliberate enquiry!

In the paper Australian Longitudes by “Wire and Wireless”, the 1921 establishment of the Western Australian border with South Australia near Deakin and the Northern Territory near Argyle, is described. These surveys were overseen by a Board then consisting of the Surveyors General of the affected States. This Board was set up under the boundary agreement signed by the heads of their respective governments on 4 November 1922. Prime Minister William Hughes signed for the Northern Territory of the Commonwealth and Acting South Australian Premier John Bice and Western Australian Premier Sir James Mitchell were the other two signatories.

The 1922 boundary agreement established the Western Australian border as a line south through the Austral Pillar near Argyle, terminating at latitude 26° south, and similarly as a line north through the Deakin Obelisk near Deakin, terminating at latitude 26° south. The agreement specifically stated that: Despite any future observations, these points shall be considered as on the boundary.

Clearly it was understood by all those involved in this undertaking, that with the technology of the 1920s that when projected south and north to latitude 26° south, these two lines would more than likely not meet.

Following the 1966 Geodetic Adjustment of Australia, when for the first time the position of all first order survey stations in Australia were established on a common datum, the projected boundary lines were calculated and found to intersect the 26th parallel 126.958 metres apart.

This distance is similar to the major dimension of most Australian sporting stadiums, so is not insignificant. However, as longitude was first determined astronomically in units of time and then converted to degrees, it represents only about 0.3 of a second of time. This is equivalent to that of the average human’s reflex time. Given the unavoidable human interaction with timing involved in 1920s astronomical measuring, the accuracy of the longitudes of the Austral and Deakin marks was at the limit of what was then achievable.

The then Director of National Mapping, Bruce Lambert, in 1967 indicated to the Board his concern about the misclose at latitude 26 south. He argued that if the interpretation of the 1922 agreement was adhered to, there will be a permanent reminder of the inaccuracies of the early surveys as is the case of the Victorian/South Australian border. However, as Western Australia had already marked and adopted some 300 kilometres of the border any such change would cause them difficulty. The Board agreed that the spirit of the 1922 agreement should be maintained. Subsequently, the Board unanimously resolved that there was no justification in seeking a variation to the 1922 agreement.

It was therefore determined that two marks be placed at 26° South Latitude; one due north of the Deakin Pillar, the other due south of the Austral Pillar. On the suggestion of Bruce Lambert the step was named Surveyor Generals Corner, and on 4 June 1968 two concrete pillars were installed. The two pillars defining the step were located from National Mapping’s first order trigonometical station Hinckley (NM/F/7) some 16 kilometres to the south-west.


Pillars at Surveyors General Corner : Left photograph shows the intersection of the projected line through the Austral Pillar near Argyle, south with latitude 26° south. Right photograph shows the intersection of the projected line through the Deakin Obelisk near Deakin, north with latitude 26° south. The two posts stand 126.958 metres (AGD66) apart.


More detail can be found in the following papers :


Porter, John (1990), Longitude 129 Degrees East, and Why it is not the Longest, Straight Line in the World, Technical Papers, 32nd Australian Surveyors Congress, Canberra, Paper 8, pp. 1–16.

Snow, T, Leighton K, Morgan L, Wheeler K, and Plaiche A (2014), The Western Australian border, where is it today?, Journal of Spatial Science, Vol. 59, No. 2, pp. 347-362.

Turnbull, David (2004), Locating, negotiating, and crossing boundaries: a Western Desert land claim, the Tordesillas line, and the West Australian border, Society and Space 2005, Vol. 23, pp. 757-770.


Compiled by Paul Wise, July 2015.