The GCAS merged datasets are the result of re-gridding and merging the sixteen GCAS TMI, radiometric and DEM surveys' located data, using a single consistent gridding algorithm and spatial origins for each data type. The gridding method used for the subject TMI grids was minimum curvature. The gridding was performed in the GDA94 geodetic coordinate system (which is consistent with the survey data capture flight lines' coordinate system) at 0.00036 decimal degrees (equivalent to 40 m cells). The grid origin of each of the 16 GCAS regions was carefully calculated to ensure that the resulting grids were co-nodular within the survey overlap regions, to eliminate or minimise the need for resampling during processing and merging. The data within the TMI grids have had a range of visualisation enhancements applied to them via filtering and magnetic tensor separation/combination, and these 21 additional pre-interpretation map products are provided in the data package as ERS grids. Explanations for why the enhancements render much value to ease of interpretation are given in the downloadable metadata description document for this data package.