Northeast Pilbara geological digital data. Digital geology of Marble Bar, Port Hedland, Nullagine and Yarrie

Brief description

These data are a digital representation of information depicted on printed maps from the Australia 1:250, 000 Geological Series produced by AGSO and the Geological Survey of Western Australia (GSWA) between 1972 and 1982. The data are gridded according to the standard Australian 1:250, 000 sheet breakup. The complete dataset is comprised of the 4 1:250, 000 sheets covering marble Bar, Nullagine, Yarrie and Port Hedland in Western Australia.
Data present include geological polygons (stratigraphic units), linear structural features (faults,
dykes, folds, trends, lineaments etc).
Polygons have a range of attributes extracted from each individual map including unit name, age and lithology, while lines and points are feature coded according to the AGSO publication Symbols Used On Geological Maps' (BMR 1989). A standard look-up table of AGSO geological codes and descriptions is available. Pilbara Data has gradually evolved from elementary 'CAD' quality data into its present topologically structured GIS format, and hence has many imperfections and inconsistencies. The spatial accuracy of data from some older maps is particularly problematical. Data has undergone only moderate checking. These map sheets were originally compiled on poor topographic bases. For a more accurate coverage of geology, use the adjusted digital version.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Source maps: the geological maps are a depiction of information acquired from interpretation (mostly airphoto), field observation, and subsequent investigation (eg sample analysis for age and rock-type determination) . Some detail may have been generalised, repositioned, or omitted from the primary data for cartographic purposes. Maps were colkoiled from unrectified photo overlays onto topographic bases supplied by Australian Government mapping authorities. Drainage and, where necessary, other topographic features (eg fence lines) were used for spatial control of the geological data (see POSITIONAL ACCURACY). PILBARA Data: data were captured from stable-base repromat used in the production of the hardcopy multicolour geological maps. Initial acquisition was by high precision scanning. Resultant raster files were warped to fit digital graticules generated using Intergraph CAM software. Affine-'- warp was used, with the four corners of each tile forming tie points. Warped raster files were then vectorised and cleaned up using Abakos Provec and Scanfix software. Further interactive editing and additional capture of Doir-t data (via data heads-up digitising over the warped raster images) was carried out using MicroStation (V4.4.023) software. Data on some tiles were block shifted to account for datum/spheroid changes (See ADDITONAL METADATA for more information). MicroStation vector data were plotted and visually checked prior to conversion to IGISI format. No attribution was attached to the MicroStation data. MicroStation vector data were translated to Arc/Info coverage format using in-house scripts and ESRI's IGDSARC utility. Attribute fields were populated using information from the printed maps and coverages were built, checked and edited. The 60 individual 1:250, 000 sheets were then all put into one geology coverage, the duplicate frames were deleted and a new graticule was created in ARC to replace the frame arcs. Extra attributes were also added.