Steep Land was first acknowledged within the Soil Conservation Act 1938 legislation as Protected Lands primarily due to land degradation impacts associated with tree clearing. Early designation of these areas was mapped by hand using topographic basemaps or interpreted from aerial photographs with 3D stereoscopes at various scales. Then acquisition of satellite data enabled all of NSW to be captured, however this was coarse and mapping of steep lands remained disputable over some areas.
In 2020 Department of Customer Services (DCS) released state-wide 5m resolution digital elevation data in the form of aerial lidar and photogrammetric point-cloud. This has been generated from a combination of 1km, 2km and 5km tiles.
Department of Planning, and Environment have utilised the source data from DCS to create the Steep Land product. Data cleansing and quality assessments have been completed.
The Steep Land 5m product has been created to effectively replace the following existing products:
* Vulnerable Lands - Steep or Highly Erodible (SHE)
* SRTM18 - Shuttle Radar
How was Steep Land determined?
Using a smoothed digital elevation model of the earth surface, a slope product was created. This was generated using the Horn 3x3 (1981) method which uses the eight pixels around the central cell to calculate the weighted gradient in north-south and east-west directions, and trigonometry to calculate the maximum slope in the aspect direction.
Having determined the slope values, accurate identification of land 18 degrees or greater and 30 degrees or greater across NSW was possible. Steep areas are identified by thresholding the slope value. Only the values of interest are extracted.
The Steep Land products are available covering NSW or in zone mosaics 54, 55, 56. They are in binary form. Please adjust the symbology as required.
18 degrees:
* 0 - Not Steep (below 18 degrees)
* 1 - Steep (areas identified as 18 degrees or greater).
30 degrees:
* 0 - Not Steep (below 30 degrees)
* 1 - Steep (areas identified as 30 degrees or greater).
Please contact data.broker@environment.nsw.gov.au for more information.
