<p style="margin-left:0px;">The AusBathyTopo 250m (Australia) 2026 Grid is an update of the national-scale depth and elevation dataset. The grid, or Digital Elevation Model (DEM), is a compilation from individual bathymetry and elevation data sources and covers the area from 92°E to 172° E and 8°S to 60° S. This includes the areas surrounding the Australian mainland, Tasmania, Macquarie Island, Norfolk Island, Christmas Island, and Cocos (Keeling) Islands. Other areas within Australia's maritime jurisdiction, including the areas surrounding Heard Island and McDonald Islands and adjacent to the Australian Antarctic Territory are not included.&nbsp;&nbsp;</p><p style="margin-left:0px;">This data package includes the national grid, a seamless 3D dataset of the land and seabed in the Australian region, an accompanying Type Identifier (TID) grid and a suite of datasets for the primary derived terrain variables that support geospatial analysis.</p><p style="margin-left:0px;">The data package was produced as part of the Resourcing Australia’s Prosperity initiative. The datasets form part of the AusBathyTopo series, providing nationally consistent seabed data to<span style="color:rgb(209,52,56);"> </span><span style="color:rgb(0,0,0);">support offshore plann</span>ing, management and environmental stewardship decisions.</p><p style="margin-left:0px;">The AusBathyTopo 250m (Australia) 2026 grid was compiled using 1542 unique data sources from multibeam echosounders, single beam echosounders, LiDAR, 3D seismic first returns, Electronic Navigation Charts (ENC) and satellite-derived bathymetry and higher-resolution regional compilations. This includes 86 new unique data sources in addition to those used in the 2024 version. Australian Hydrographic Office (AHO) supplied ENC tile spot depths provide broad scale bathymetry coverage across the dataset. Airborne LiDAR bathymetry and satellite-derived bathymetry data cover nearshore and coastal regions, whilst multibeam and single beam data cover shallow and deep-water areas. In areas where no sounding data are available, the bathymetry is provided by an amended surface derived from 2-arc minute ETOPO (Smith and Sandwell, 1997) and 1-arc minute ETOPO (Amante and Eakins, 2008) satellite altimetry data. The Geoscience Australia-developed National Intertidal Digital Elevation Model (NIDEM) (<a href=" http://dx.doi.org/10.26186/5c4fc06a79f76"><span style="color:rgb(70,120,134);"><u> http://dx.doi.org/10.26186/5c4fc06a79f76</u></span></a>) was used to improve continuity between bathymetry and topography. Terrestrial elevation data was provided by the Shuttle Radar Topography Mission (SRTM) (<a href=" https://pid.geoscience.gov.au/dataset/ga/72759"><span style="color:rgb(70,120,134);"><u> https://pid.geoscience.gov.au/dataset/ga/72759</u></span></a>).</p><p style="margin-left:0px;">This new AusBathyTopo grid represents decades of data collection, analysis, investment and collaboration from Australia’s seabed mapping community and is a significant improvement on previous compilations.</p><p style="margin-left:0px;">This dataset is not to be used for navigational purposes.</p><p style="margin-left:0px;"><u>Source Data Types</u></p><p style="margin-left:0px;">The accompanying Type Identifier (TID) grid identifies the source data type contributing to each cell within the AusBathyTopo 250m (Australia) 2026 grid. Each cell is assigned a TID-code corresponding to the sensor type used to derive the depth or elevation value. Where overlapping data from multiple sensor types exists, the highest quality source was retained.</p><p style="margin-left:0px;">TID codes follow GEBCO standards (<a href=" https://www.gebco.net/gebco-tid-grid"><span style="color:rgb(70,120,134);"><u> https://www.gebco.net/gebco-tid-grid</u></span></a>).</p><p style="margin-left:0px;"><u>GEBCO Data Type and Definitions:</u></p><ul><li>Land (code 0).<strong> </strong>Definition: NA.</li><li>SBES<strong> </strong>(code 10).<strong> </strong>Definition: Single beam - depth value collected by single beam echo-sounder.</li><li>MBES<strong> </strong>(code 11).<strong> </strong>Definition: Multibeam - depth value collected by multibeam echo-sounder.</li><li>ENC, Elevation<strong> </strong>(code 14).<strong> </strong>Definition: ENC sounding - depth value extracted from an Electronic Navigation Chart (ENC).</li><li>LiDAR (code 15).<strong> </strong>Definition: LiDAR - depth derived from a bathymetric light detection and ranging sensor.</li><li>Coast, NIDEM, SDB (code 16). Definition: Depth measured by optical light sensor.</li><li>Pre-generated grid (code 70). Definition: Pre-generated grid - depth value is taken from a pre-generated grid that is based on mixed source data types, e.g. single beam, multibeam, interpolation etc.</li></ul><p style="margin-left:0px;"><u>Bathymetric Derivatives</u></p><p style="margin-left:0px;"><span style="color:rgb(0,0,0);">To support geospatial analysis, this data package includes a series of derived datasets: aspect, contours, hillshade, rugosity, slope. These datasets are generated from the AusBathyTopo 250m (Australia) 2026 grid using ArcGIS v3.7.0 Spatial Analyst Tools.</span></p><p style="margin-left:0px;">The parameters used to generate the derived datasets were:</p><ul><li>Slope: Output measurement – Degrees; Method – Geodesic; Z unit – Meter.</li><li>Aspect: Method – Geodesic.</li><li>Contours: 250m and 500m intervals.</li><li>Hillshade: Azimuth – 315°; Altitude – 45°.</li><li>Rugosity:&nbsp; Z Unit – Meter; Planar Area Type – Arc-Chord.</li></ul><p style="margin-left:0px;"><u>Data Packages</u></p><ul><li>AusBathyTopo_Australia_2026_250m.zip contains the AusBathyTopo and TID grid, and a data source list.</li><li>AusBathyTopo_Australia_2026_250m_derivatives.zip contains derivatives of the grid including contours, aspect, hillshade, slope and rugosity.</li></ul>