GDA Map Information Block Guidance Notes

DSE have developed information suitable for the annotation of GDA compliant hardcopy maps and plans. The information should be used by map producers and publishers in whole or part (depending on the application) as a resource to ensure any information provided to users on or preceding map/plan sheets in book form is clear and unambiguous and is consistent with national and state specifications for the transition to the GDA.

A version of this information and explanation follows and features:

1. The official, nationally used GDA logo (downloadable from theICSM site) which provides clear identification of map and plan products;
2. GDA heading and border in red to attract the readers attention;
3. A statement that the new datum supersedes the previous datum used in Victoria;
4. A statement to alert GPS users that geographic references (latitudes and longitudes) on GDA compliant maps are the same as geographic references produced by receivers configured to output in the World Geodetic System 1984 (WGS84) datum. GPS receivers affected by Selective Availability may of course deviate from true positions shown on maps and plans that are GDA compliant by around 100m;
5. Datum conversions to guide map users between the Australian Geodetic Datum 1966 and the Geocentric Datum of Australia. The conversion values and accuracy estimate are applicable for Victoria only. Victoria is south of the equator and has negative latitude values. The words numerical value and increase have been used to avoid confusion in applying corrections to latitude values.
   
   The Northing and Easting shift values relate to projection coordinates for the Universal Transverse Mercator projection. Projection coordinates relating to the AGD66 are referred to as Australian Map Grid (AMG) coordinates and Map Grid of Australia (MGA) for the Geocentric Datum of Australia. The shift values shown that are applicable to the centres of UTM zones 54H and 55H.
   
   The new GDA does not affect the current Australian Height Datum (AHD) and as such no reference has been made to the vertical dimension. This approach has been recommended by the ICSM to avoid confusion. GPS users may notice variations between heights shown on the AHD and that produced from receivers caused by Selective Availability and/or the separation of the geoid and ellipsoid;
6. Examples have been shown which depict the application of conversion values for geographic and projection coordinates in particular zones;
7. The Intergovernmental Committee on Surveying and Mapping (ICSM) are the peak body coordinating the introduction of the GDA and interested users should contact this organisation for clarification of issues relating to the change in datum; and,
8. Consideration should be given to the application of the words GDA onto the body of map sheets if it is the practice of users to fold or cut out portions of the map, hiding or discarding the GDA information block.