NTData (digital geology of the Northern Territory)

Brief description

These data are a digital representation of information depicted on printed maps from the Australia 1:250 000 Geological Series produced by Australian Geological Survey Organisation (AGSO) and the Northern Territory Geological Survey (NTGS) between 1963 and 1998. The data are in a tiled format and are not seamless, although basic edgematching has been done where possible. Tiles are arranged according to the standard Australian 1:250 000 sheet breakup. The complete dataset is comprised of the 90 tiles covering the Northern Territory. Available as CD-ROM package (transfer fee A$99.00/cdrom) or free to download from http://www.ga.gov.au/minerals/research/national/thorium/index.jsp. Available in arc/info, mapinfo and microstation formats. Individual datasets contained in records #61181 - #61271

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 compiled 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). NTData: 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 generated using Intergraph CAM software. Affine-1 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 point 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 GIS format. No attribution was attached to the MicroStation data. MicroStation vector data were translated to Arc/Info coverage format using in-house scripts and ESRIs IGDSARC utility. Attribute fields were populated using information from the printed maps and coverages were built, checked and edited. Arc/Info coverages were then written as both double and single precision uncompressed Arc Export format.Arc Export files were translated into MapInfo tables using MapInfo Professional (V4.02) and ArcLink (V3.1.2).