Datums & your GPS

Brian Fleming raises some important issues regarding Global Positioning Systems, the next generation of topographic maps (which work together) and using GPSs while birding .

As GPS owners know, their units have a wide range of datums to choose from.  All current GPS devices should have the Geocentric Datum of Australia 1994 (GDA) as an option.  This is to be the standard datum for Australia I believe.

As Brian mentions, old maps have a different datum (often Australian Geographic Datum 1966) to that now used on new topographic maps.  Depending on the datum you use your GPS can give a slightly inaccurate locality reading.  Hence it's important to make sure you datum matches the map you are basing your survey on.

In Victoria we are lucky to now have a new series of 1: 25 000 topographic maps which use GDA.  This means GPS users can easily choose the correct datum when using the relevant map.

Atlassers in Victoria are being encouraged to use GDA as the primary datum wherever possible.  This is because the mapping products that are now being produced by them use GDA as the standard datum.

If you have ever completed Birds Australia Atlas sheets or Atlas of Victorian Wildlife recording sheets, then you know that each asks you to indicate what datum you have used to determine your locality information.

There is plenty of useful information around on this issue and I've provided a few of the better web sites below.

1. Datums and Coordinates
http://www.ga.gov.au/geodesy/datums/aboutdatums.jsp

2. Geocentric Datum of Australia (GDA)(Federal Government site)
http://www.icsm.gov.au/icsm/gda/

3. Geocentric Datum of Australia (Land Victoria site)
http://www.land.vic.gov.au/land/lcnlc2.nsf/childdocs/-47498102F8201F80CA256E4C00187958-3E2744A50EFE9587CA256E4C0018796A-731A29BE0E290F9A4A256A250008E70F?open

3. GDA and topographic maps (Federal Government site)
http://www.icsm.gov.au/icsm/gda/mapsgda.pdf

4. Moving to GDA (Dept. Sustainability & Environment, Victoria site)
http://www.dse.vic.gov.au/DSE/nrenptm.nsf/LinkView/FEB2525DAABF9A89CA256F900016F74946BCC6FBC478C5D6CA256F93001FB159

The 'GPS - A Guide for users' can also be found via this site.

Martin O'Brien
Threatened Species & Communities Section
Department of Sustainability and Environment
2/8 Nicholson St. East Melbourne  3002
Australia

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