ANZLIC Identifier: Unassigned (Derivative of ANZNT0001000070)
Title: Pellew 250K Geology
Custodian: Northern Territory Geological Survey
Jurisdiction: Northern Territory
Data on NT geology supplied by Australian Geological Survey Organisation (AGSO), now Geoscience Australia (GA) at the following scales: 1:2 million and 1:250 000 The Digital Capture of 1:250 000 Geological Maps of the Northern Territory - 'NTData' - is a collaborative venture between the Australian Geological Survey Organisation (AGSO) and the Central Land Council (CLC), in cooperation with the Northern Territory Geological Survey (NTGS).
This data is a digital representation of information depicted on printed maps from the Australia 1:250 000 Geological Series produced by AGSO and the Northern Territory Geological Survey (NTGS) between 1963 and 1997. The data are in a tiled format and are not seamless, although basic edge-matching has been done where possible. Tiles are arranged according to the standard Australian 1:250 000 sheet break-up. The complete dataset will be comprised of the 87 tiles covering the Northern Territory; a one tile verge all around may be added in the future. Data present include geological polygons (stratigraphic units), linear structural features (faults, dykes, folds, trends, lineaments etc.), and point features (dips, mines, age localities 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. NTData 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 due to limited resources.
The Pellew Geology 250K Map has been modified to conform to the current NTGS Data Dictionary and symbology standards.
Projection: MGA53
Datum: GDA94
Geographic Extent Polygon(s): (expressed as decimal degrees) -15.00 136.50, -15.00 138.00, -16.00 136.50, -16.00 138.00
Bounding Coordinates:
North Bounding Coordinate: -15.00
South Bounding Coordinate: -16.00
East Bounding Coordinate: 138.00
West Bounding Coordinate: 136.50
Beginning Date: Not Known
Ending Date: Current (Original Compilation: 1963. Date of NTGS Conversion: 2014)
Progress: Complete
Maintenance and Update Frequency: As required, but is not included in 2019 NTGS Project Schedule
Stored Data Format: Digital Microstation DGN, MapInfo .TAB, ArcGIS .SHP Available Format Type: Digital Microstation DGN, Mapinfo .TAB, ArcGIS .SHP
Access Constraints: None
Source maps: the geological maps are a depiction of information acquired from interpretation (mostly air photography), field observation, and subsequent investigation (e.g. 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 Commonwealth mapping authorities. Drainage and, where necessary, other topographic features (e.g. 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 software. Data on some tiles were block shifted to account for datum/spheroid changes (See ADDITIONAL 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. Attribute fields were populated using information from the printed maps and coverages were built, checked and edited.
The digital Pellew Geology 250K Map layers have been modified to conform to the NTGS Data Dictionary and NTGS Symbology standards (which are derived from Stewart, A. J et al, 1989, Symbols used on Geological Maps, BMR, Canberra, ACT). Geological attribution has generally not been altered, although obvious anomalies in the data or symbology have been corrected by NTGS Project Geologists or Spatial Administrators where encountered. Attributes have also been updated with current Geoscience Australia feature codes, and the data tables have been re-projected to the GDA94 Datum. The geological polygons have been coloured to matched to original Pellew Geology 250K production map.
An accurate assessment of horizontal accuracy is not possible because the history of the original source information and subsequent revisions by the States is not fully known. However during construction of the dataset we observed a range of errors/anomalies which we believe may be due to:
The NTGS modified datasets retain the qualifiers describe above.
Attributes are mostly a representation of information on the source maps and should be viewed in that context - some of the information/interpretation is more than 35 years old and may be incorrect/outdated. Attributes are tile specific - for example the same geological unit on separate tiles may have different lithological descriptions, ages and possibly even names. This is a reflection of the knowledge/information available at the time of production of the source map.
General: geological units and linear structures such as faults and folds were largely interpreted from airphotos in conjunction with field observation/measurement, and sample collection and analysis. The reliability diagram on the printed geological source maps gives some (basic) indication of the level of work undertaken. Most of the source maps have accompanying Explanatory Notes which provide much more detail about the geology and interpretations. Point data attributes, e.g. strike and dip values, have been extracted from the map and thus may include cartographic generalisation and error (maps were however subject to considerable checking and editing during their production, and can be considered a good facsimile of the primary data).
The NTGS modified datasets retain the qualifiers describe above, with the addition of the following:
Data have been checked visually on plots and for topological consistency using in-house routines and MapInfo GIS software. As much as possible, every effort has been made to ensure that the accuracy and standards of the source maps have been maintained.
The NTGS modified data conforms to current NTGS Data Dictionary, file naming conventions and symbology standards.
Completeness:
Coverage: because the geological maps are the only source for NTData, not all attributes are complete for all elements or tiles. In some cases (e.g. the age, name and genealogy of stratigraphic units), information may be outdated and may also be inconsistent between tiles. The latest information is often available in various GA and/or NTGS databases, e.g. the GA Stratigraphic Names database, but this has not been incorporated into NTData tiles at this time.
Classification: completeness and consistency of classification needs to be considered in the context of the time span of the source geological maps (1963-1997) and the highly interpretative nature of the discipline. Broadly similar classification and measurement techniques have been applied to geological map compilation for many years, however resultant data does reflect individual geologists ideas and preferences. The classification of boundaries, faults etc. (accurate, approximate, concealed, inferred) for example is not particularly consistent and therefore needs to be treated with caution. Additionally, maps produced since the early 1980s will have been subject to more field checking, and may have had the advantage of remotely sensed data (Landsat and geophysical images). In general, one can say that modern maps (and hence the digital data derived therefrom) contain significantly more detail (are less generalised and have greater subdivision of geological units) than older maps.
Verification: there is no consistent record of the extent of field observation as opposed to remote (air photography) interpretation. However the frequency of measured sites on maps, e.g. dips of bedding etc., is a reasonable indicator of field activity/verification. More information can be found in Explanatory Notes which were produced in conjunction with the geological maps.
Contact Organisation: Northern Territory Geological Survey
Contact Position: Manager, Geoscience Business Systems
Postal Address: GPO Box 4550
City: Darwin
State: NT
Country: Australia
Postcode: 0801
Telephone: +61 8 8999 6443
Facsimile: +61 8 8999 6824
Electronic Mail Address: geoscience.info@nt.gov.au
Metadata Date: 22 November 1999
NTGS updates:29 July 2019
© Northern Territory Government (Northern Territory Geological Survey) 2017
The Northern Territory Government supports and encourages the dissemination and exchange of its information. The copyright in this publication is licensed under a Creative Commons Attribution 4.0 International Licence. Under this licence you are free to use this publication in accordance with the licence terms without having to seek our permission. You must keep intact the copyright notice and attribute the Northern Territory Government as the source of the publication.
Please give attribution to: © Northern Territory Government (Northern Territory Geological Survey) 2017.
We also request that you observe and retain any copyright or related notices that may accompany this material as part of the attribution. This is also a requirement of the Creative Commons Licences.
While all care has been taken to ensure that information contained in this publication is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of its information. The Northern Territory of Australia gives no warranty or assurance, and makes no representation as to the accuracy of any information or advice contained in this publication, or that it is suitable for your intended use. You should not rely upon information in this publication for the purpose of making any serious business or investment decisions without obtaining independent and/or professional advice in relation to your particular situation. The Northern Territory of Australia disclaims any liability or responsibility or duty of care towards any person for loss or damage caused by any use of, or reliance on the information contained in this publication.
NTGS Data Dictionary 2014, NTGS Symbology Standards 2007
Pellew, Northern Territory (First Edition) 1963. 1:250 000 geological map series, SD 53-16. Bureau of Mineral Resources, Australia, Canberra.
Pellew, Northern Territory (First Edition) 1963. 1:250 000 geological map series explanatory notes. SD 53-16. Bureau of Mineral Resources, Australia, Canberra.
Refer to AGSO for coverage availability, Northern Territory only have partial coverage. Stirzaker, J., 1996. NTData. Technical papers of the Mapping Sciences 96 Conference. Mapping Sciences Institute, Australia, Canberra, 1996, 249-258.