9541_r

The polygons in this dataset are a digital representation of the distribution or extent of geological units within the area. Polygons have a range of attributes including unit name, age, lithological description and an abbreviated symbol for use in labelling the polygons. These have been extracted from the Rock Units Table held in the Department of Natural Resources, Mines and Energy Merlin Database.

To display the geology polygons which define the extent of rock units.

Data captured at 1:37 500 scale. The data set is sourced from the Department's Geoscience and Resources Database (GRDB), a component of the Mineral and Energy Resources Location and Information Network (MERLIN) corporate database.(GRDB), a component of the Mineral and Energy Resources Location and Information Network (MERLIN) corporate database.

NOTE: GEOLDATA was in most cases compiled based on Datum AGD66. The map tile coverages so compiled have now been projected to geographics based on Datum GDA94. Consequently the boundaries for these map tiles will not conform to the Latitude and Longitude graticule based on Datum GDA94.

An accurate assessment of the horizontal accuracy is not possible, because the history of the original source information of each line and subsequent revisions are not fully known. Apart from uncertainties in interpretation and location of these features on the ground or on various images, other errors can result from inaccurate topographic bases, spheroid or datum differences, map compilation processes and subsequent digitising. This dataset was compiled on photo-overlays on unrectified aerial photographs ranging from 1:25000 to 1:85000 scale. Maps were compiled from these overlays onto topographic bases, using drainage and cultural features for spatial control. Assuming the feature had been correctly interpreted and located on the aerial photographs, the estimated positional error is estimated at 1mm at the respective scale. To that could be added at least another 1mm due to misfits between the air-photo and the base because of distortion in the photograph or inaccuracies in the base. Therefore, at best,  the total positional error due to map production processes is about +/- 170m from 1:85000-scale photographs and +/- 50m from 1:25000 scale. It is stressed that this does not take into account the uncertainties in interpretation and location of these features mentioned above, so that the actual error is often much greater than listed.