Geology of the Georgetown

Brief description

These data are a digital representation of information depicted on the printed map of the Georgetown 1:250 000 Geological Series produced by AGSO and the Geological Survey of Queensland (GSQ) in 1985 (1st edition). Data present include geological polygons (litho-stratigraphic units), linear structural features (faults, dykes, folds, trends, lineaments etc), and point features (mines, structural points etc). Polygons have a range of attributes extracted from each individual map including unit name, age and lithological description, 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 associated descriptions is available (see ADDITIONAL METADATA). The data has gradually evolved from elementary CAD quality data into its present topologically structured GIS format, and hence has many imperfections and inconsistencies. Data has undergone rigorous validation and testing that includes over 80 different tests. See ADDITIONAL METADATA for more information on the data standards used.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Source: The geological maps are a depiction of information acquired from interpretation, field observation, and subsequent investigation. Some detail may have been generalised, re-positioned, or omitted from the primary data for cartographic purposes. Maps were compiled from unrectified photo overlays onto topographic bases supplied by the Commonwealth mapping authorities. Drainage and other topographic features were used for spatial control of the geological data. Data capture: Data were captured from stable-base repromat used in the production of the hardcopy multi-colour geological maps. Initial acquisition was by high precision scanning. Resultant raster files were warped to fit digital graticules. Affine-1 warp was used, with the four corners of each tile forming tie points. Warped raster files were vectorised and cleaned, followed by interactive editing and additional capture of point data (via data heads-up digitising). Vector data were plotted and visually checked prior to conversion to GIS format. Translation from MicroStation to ArcInfo format was facilitated using in-house scripts and IGDSARC utility. Attribute fields were populated using information from the printed maps. Coverages were built for topology, checked and edited. Upgrade: Data are unprojected from UTM projection into geodetic coordinate system. In addition, a datum-shift was performed from AGD66 to GDA94. Coverages were edge-matched with the surrounding tiles, where data was available. While, in general, features at the coverage boundaries matched, sometimes it was necessary to carry out limited interpretative work. Attributes were appended and existing modified as per specifications in the AGSO GIS Data Dictionary. Stratigraphic unit names were validated against records in AGSO's Stratigraphic Index database. Where superseded, they were replaced with the current names. Additional attributes, from the database, were added to all geological units with a known stratigraphic unit name.