GDA : Frequently Asked Questions

View the GDA SlideShow

Download free GDA brochure

With GPS now common, many people use coordinates than formerly. These come as either latitude and longitude, or East and North. The most common example of this, is how Australia changed its mapping, navigation and positioning systems to a new datum - the Geocentric Datum of Australia 1994, or GDA94. Put simply, all coordinates - latitude, longitude, east and north - will alter by between 130 and 170 metres each. This change took place during 2000-2001, but still impacts on everyone who uses

The changeover was adopted by both state and commonwealth governments and means, in practice, that all Australians need to adjust.

The government rationale was to bring our map systems into line with international usage, and with modern positioning technologies, particularly the Global Positioning System (GPS). A point located relative to the new datum will be approximately 200metres south-west of the point denoted by the same latitude and longitude on the previous datum.

Conversion does NOT mean that permits, structures or points will move. However, wherever locations are mapped or stored in latitude and longitude, or in east and north, those coordinate values WILL change. Nor will it affect ownership of permits, leases, etc. But it WILL open significant risks of confusion and 200m errors.

The new datum - the base from which coordinates are measured - is named GDA94 (or just GDA). Maps based on a Transverse Mercator projection from this datum will be referred to as MGA, or Map Grid of Australia. GDA and MGA will replace AGD(84) and AMG respectively.

Prevention is better than cure.

With planning, and with assistance where you cannot divert the resources yourself, changeover to GDA is easily managed. Geoproject Solutions hopes this information will be useful, and would be pleased to provide any further assistance.

Check list for minimising GDA hassles

When must information lodged with government be GDA-based?
Information for colleagues / staff / management Make clients aware of your plans
Management systems:
Quality system affected?
Spatial data stored in GIS or CAD systems:
Can your GIS/CAD/Seismic software transform?
Data being acquired
Make sure datum for incoming data is known. When will suppliers change to GDA?
Paper charts and plans which you need to continue using
How will they be marked to avoid mistakes by future users?
Supplying digital data
How will recipients be advised as to datum? Changeover date
Mineral exploration permits
Ensure familiarity with DM&E schema, especially graticular licenses bounded by regular latitude and longitude values.

Approximate conversion factors

This map shows the differences in coordinates at specific locations.

Conversion of smaller scale maps and for preliminary check of conversion routines.
Intended for
maps and data derived from points for which AGD84/AMG positions have been provided by WA state government authorities.
Other positions
Not appropriate to positions based on other networks, e.g Landstar and OmniSTAR

Useful websites for further information

GDA : Frequently Asked Questions

View the GDA SlideShow

Download free GDA brochure


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