Impervious surfaces were derived from two existing mapping products, producing six classes of impervious area: Buildings, Roads, Railways, Roads and Railways, Airports and Aerodromes, Stormwater Infrastructure.

Impervious Surfaces associated with buildings were derived from the Geoscape® Buildings Theme, which provides polygon representations of every building in Australia with a roof area equal to or greater than 9m2. Building polygons from the Greater Sydney Region were extracted and used to create the ‘Buildings’ feature.

Impervious Surfaces not associated with buildings were derived from the NSW Land Use Map 2017 (inclusive of the draft Land Use Mapping for the Sydney Metropolitan Region), which provides land use mapping for NSW at a 1:10,000 reliability scale, based on the Australian Land Use and Management Classification Code. This layer was used to generate the Roads, Railways, Roads and Railways (polygons reclassified during QC) Airports and Aerodromes, and Stormwater Infrastructure features.

Once both sets of features had been generated, they were intersected with LGA to aid in computation and provide additional map utility. Following this, any overlap between the Buildings features and the Land Use features was corrected using the Erase Function, before the layers were combined using the union function, and dissolved by LGA and feature class to provide LGA-level breakdowns of the prevalence and providence of impervious areas.