This dataset shows land parcels within grassland and annual cropping areas which have an average slope of less than 10 degrees. Polygons are attributed into 3 slope classes: less than 5 degrees mean slope; 5 - 7 degrees mean slope; 7 - 10 degrees mean slope.
This layer is derived from LINZ parcel data and the Manaaki Whenua - Landcare Research 15m Digital Elevation Model (DEM). This DEM was originally derived from LINZ 20m contours and processed to maximise the accuracy of slope and aspect calculations for use in topographic correction to the spectral reflectance in satellite imagery. A slope layer was derived from the DEM and zonal statistics were calculated for each land parcel (excluding Road and Hydro parcels) to determine the average slope. Parcels with an average slope of less than 10 degrees were selected. This layer was clipped to the extent of low and high-producing grassland and annual cropland (derived from the LUCAS 2016 v006 land use map) and the Public Conservation Land area was removed. Finally, the remaining land parcels were classified into mean slopes of less than 5 degrees, 5 to 7 degrees and 7 to 10 degrees.
*Data Quality* This layer is likely to have captured some land parcels which have some type of reserve status or other restriction which means that livestock grazing is not permitted. It is therefore likely to be an over-estimate of the land area which would be affected by the proposed stock exclusion regulation. Conversely, some rural land parcels are large and include intensively grazed flat areas and very steep hill-country areas. It is likely that some of these intensively grazed part-parcels will not be covered by the low-slope extent because the average parcel slope is greater than 10 degrees.
The DEM used for this slope calculation has been judged to be the best available nationally consistent DEM for identifying low slope areas which are likely to be intensively grazed. It is recognised that the use of a high resolution LiDAR-based DEM would yield a different result and may require the adjustment of slope thresholds to cover the required area of intensive use. As part of the "Action for Healthy Waterways" consultation feedback is being sought on whether the slope threshold for identifying the stock exclusion area should be set at 5, 7 or 10 degrees using this DEM.
*Attributes* "id" = LINZ Parcel id; "slope_mean" = mean parcel slope; "slope_class" = (1_lteq5: slope_mean <= 5 degrees) (2_5to7: slope_mean between 5 and 7 degrees) (3_7to10: slope_mean between 7 and 10 degrees)