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GEODATA 9 Second Flow Direction Grid (D8-9S)

Note: This metadata describes the dataset in accordance with the ANZLIC (Australia New Zealand Land Information Council) Core Metadata Guidelines Version 2.


Dataset citation

ANZLIC unique identifier: ANZCW0703012015

Title: GEODATA 9 Second Flow Direction Grid (D8-9S)


Custodian

Custodian: Geoscience Australia

Jurisdiction: Australia


Description

Abstract:

The GEODATA 9 Second Flow Direction Grid is a regular grid of surface flow directions accompanying the GEODATA 9 Second Digital Elevation Model Version 3. It ascribes to each DEM point one of eight cardinal directions (E, SE, S, SW, W, NW, N, NE) denoting the direction of surface flow from each grid point to one of its eight immediate neighbours. These directions are coded according to standard Arc/Info convention with (1=E, 2=SE, 4=S, 8=SW, 16=W, 32=NW, 64=N, 128=NE). If there is no downstream neighbour the cell is given the value 0 denoting a sink. The main applications of flow direction grids are automated delineations of streamlines and catchment boundaries. Flow direction grids are also well suited to the calculation of convergent flow for various hydrological modelling applications associated with streamflow. The 9 Second Flow Direction Grid is derived from the multi-flow direction grid produced by the ANUDEM procedure used to calculate the 9 Second DEM. This was done by choosing the principal stream direction at each multi-flow grid point as defined primarily by the hierarchy field for the GEODATA TOPO-250K streamlines and secondarily according to the stream name. Flow direction grids can be derived by computing the aspect of the downslope direction at each DEM grid point from the relative heights of the neighbouring grid points. However, in low relief areas, which abound in large parts of Australia, the downslope direction is not always accurately defined from the neighbouring DEM points. This can lead to significant errors in delineating streamlines and catchment boundaries. The flow direction grid associated with the production of the 9 Second DEM by the ANUDEM program always adheres to the flow directions implicit in the supporting streamline data, no matter how flat the local relief. The Flow Direction Grid is therefore released with the 9 Second DEM to ensure that streamlines and associated catchments can be accurately delineated everywhere.

ANZLIC search words:

  • LAND Topography Models

Spatial domain:

locality map

Geographic extent name: AUSTRALIA EXCLUDING EXTERNAL TERRITORIES - AUS - Australia - Australia

Geographic extent polygon: 112 -9, 154 -9, 154 -44, 112 -44, 112 -9,

Note: The format for each Geographic extent name is: Name - Identifier - Category - Jurisdiction (as appropriate) See GEN Register

Geographic bounding box:
North bounding latitude: -9 °
South bounding latitude: -44 °
East bounding longitude: 154 °
West bounding longitude: 112 °

Data currency

Beginning date: 2005-07-01

Ending date: 2008-06-30


Dataset status

Progress: Complete

Maintenance and update frequency: Not Known


Access

Stored data format:
DIGITAL - img ERDAS Imagine image Imagine Geographic GDA94
DIGITAL - asc ASCII text Geographic GDA94
DIGITAL - ArcGIS-grid ArcInfo grid Geographic GDA94
DIGITAL - ers ER Mapper raster dataset ER Mapper Geographic GDA94
Available format type:
DIGITAL - ArcGIS-grid ArcInfo grid Geographic GDA94
DIGITAL - asc ASCII text Geographic GDA94
DIGITAL - img ERDAS Imagine image Imagine Geographic GDA94
DIGITAL - ers ER Mapper raster dataset ER Mapper Geographic GDA94

Access constraints:

The data are subject to Commonwealth of Australia Copyright. A licence agreement is required and a licence fee is also applicable for packaged data (included in the purchase price).

Free Data Download

Data quality

Lineage:

The 9 Second DEM was calculated by the ANUDEM procedure in overlapping tiles corresponding approximately to the standard 1:1M topographic maps for Australia. At the same time the ANUDEM procedure calculated a multi-flow direction grid corresponding to each DEM tile. These multi-flow grids respect the full distributary structure in the GEODATA TOPO-250K streamline data, but such multi-flow grids are not amenable to analysis by standard GIS packages. The flow direction grid distributed with the 9 Second DEM was therefore derived from the multi-flow direction grid produced by ANUDEM by choosing the principal stream direction at each multi-flow grid point as defined primarily by the hierarchy field for the GEODATA TOPO-250K streamlines and secondarily according to the stream name. The flow direction grids for each overlapping tile were merged by abutting adjacent grid tiles at the mid-lines of each overlapping pair. These flow directions were edited to remove circularities that occasionally arose in this process.

Positional accuracy:

The density of the topographic source data for the 9 Second DEM and the 9 second grid spacing means that the flow direction grid can be considered to have a scale of 1:250 000. The notion of positional accuracy for the longitude and latitude values given in the data is not applicable as the grid locations are generated as part of the grid generation process.

Attribute accuracy:

The mean distance of the gridded stream lines, as encoded in the 9 second DEM flow direction grid, is about 60m or one quarter of the width of one grid cell. Approximately 95% of the gridded streamlines lie within 125 metres of the mapped streamline network and virtually all are within 270 metres.

Logical Consistency:

The 9 Second Flow Direction Grid has one flow direction value for each grid cell. Cells with no downstream neighbour are denoted as sink points. The elevation of the associated 9 Second DEM at each sink point is a local minimum of the elevation grid.

Completeness:

The Flow Direction Grid covers all land areas including all islands defined by the GEODATA COAST 100K data.


Contact information

Contact organisation: Commonwealth of Australia (Geoscience Australia) (GA)
Contact position: Manager Client Services
Mail address: Cnr Jerrabomberra Ave and Hindmarsh Dr
Mail address: GPO Box 378
Locality: Canberra
State: ACT
Country: Australia
Postcode: 2601
Telephone: 02 6249 9966
Facsimile: 02 6249 9960
Electronic mail address: sales@ga.gov.au

Metadata information

Metadata date: 2013-03-08


Additional metadata

Metadata reference XHTML: http://www.ga.gov.au/meta/ANZCW0703012015.html

Metadata reference XML: http://www.ga.gov.au/meta/ANZCW0703012015.xml

The 9 Second Flow Direction Grid is produced in standard ESRI grid format to permit standard hydrological applications. The ESRI Flow Direction Grid (D8) is an integer raster where values represent flow direction from the centre. Values are;

1 East

2 South East

4 South

8 South West

16 West

32 North West

64 North

128 North East

0 Indicates a sink

For further Information, refer to the GEODATA 9 Second DEM Version 3 and Flow Direction Grid User Guide (UserGuide.pdf), supplied with the product or available at www.ga.gov.au

For further information on the ANUDEM program Version 5.2.2 used to calculate the Flow Direction Grid (D8-9S) and Digital Elevation Model (DEM-9S) please contact the Fenner School of Environment and Society:

Fenner School Publications/Software

Fenner School of Environment and Society

Australian National University

CANBERRA ACT 0200

e-mail: publications@fennerschool.anu.edu.au

Internet: http://fennerschool.anu.edu.au/publications/software/

Authors:Hutchinson, M.F. Stein, J.L. Stein, J.A.
SPATIAL INFORMATION FOR THE NATION