What is the difference between GDA94 and WGS84?
WGS84 is the datum used by the GPS system, and also for many small scale maps (e.g. maritime charts). When GDA94 was defined, it was a requirement that coordinates of points in these 2 systems should be within a metre of each other. This was achieved, and is generally still the case in 2000. The spheroids used for WGS84 and GDA84 are also almost identical, and both systems are geocentric. Thus for most mapping, exploration and GIS uses, WGS84 and GDA94 coordinates will be the same. If you use a GPS receiver (alone, or with a differential service) and the GDA datum is not a built-in option, you can select WGS84. For precise surveys, however, the difference between WGS84 and GDA94 may be significant, and changes slowly over time. There are two reasons: • WGS84 is recalculated on a world-wide basis every few years for GPS control • Tectonic movements of the Australian plate affect WGS coordinates for Australian stations, but do not affect the GDA coordinates (see answer below “How will co
