Johnston Geodec Centre - NT

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).