A NHT (National Heritage Trust) funded project headed by the NRM Cradle Coast to delineate coastal areas with potential to contain Acid Sulfate Soils (ASS). The dataset forms part of the larger project pertaining to ‘Tasmanian Acid Sulfate Soils Information’ (TASSI) with the aim of providing better awareness to stake holders and planners in regards to the distribution of Acid Sulfate Soils in coastal environments of Tasmania. Coastal environment for the sake of the TASSI project was defined as the zone between 0 and 20m AHD. The dataset comprises polygons mapped at a variety of scales in different parts of the state (mostly at 1:25,000 or 1:250,000) and geo-referenced to the GDA94 datum. Each polygon is attributed with a probability rating (high, low or extremely low) that indicate a polygons potential to contain ASS as well as a descriptor/code which describe the ASS landscape that a polygon represents. The descriptor/code pertains to the Atlas of Australian Acid Sulfate Soils (developed in part by CSIRO and used on the ASRIS website, http://www.asris.csiro.au ). Ancillary dataset information that were used to model and derive the probability ratings and subsequent codes are embedded within the dataset attribute table.

1:25,000 MRT geology map sheets (as available at June 2008), 1:250,000 state wide MRT geology digital map; Detailed soils maps (Coal River Valley, Flinders Island, Foo Choo Flats, King Island, Montagu Swamp, Mowbray Swamp, NW Coast, Tomahawk, Waterhouse), 1:100,000 Reconnaissance soil maps, 1:500,000 Dominant soil order map of Tasmania; Multiresolution Index of Valley Bottom Flatness (derived from the Tasmania 25metre Digital Elevation Model); Tasmanian Quaternary Coastal Sediments Polygon Map; 1:25,000 TASVEG; 1:25,000 Hydrographic dataset. Map units conducive to ASS were derived from the above ancillary datasets (notably geological and soils units as well as hydrographic units representing swamps and wet areas) and used to form a predictive cartographic model. Units were given likelihood ASS weightings which were then combined/overlayed with one another to give a total accumulated ASS probability score. Where a high accumulation of map units were apparent; indicated an area more likely to have ASS potential. A lack of accumulated map units indicated an area less likely to have ASS potential. The resulting accumulated areas were then classified in accord to the Atlas of Australian Acid Sulfate Soils using existing digital ancillary information and that garnered from field work reconnaissance. The model outputs were field checked over several months, where the model was recalibrated and re-run if inaccuracies were found. The final output is considered to be an accurate representation of Coastal Acid Sulfate Soils using the best digital information at hand at the time as well as input from historic and current field work reconnaissance.

Position Accuracy: Each polygon is attributed with the ancillary dataset(s) that was used to delineate an ASS area. The dataset(s) used to delineate an ASS area gives an indication of the scale that was modelled for that particular ASS area. However, it is generally accepted that the final dataset uses the line work of the 1:25,000 Hydrographic dataset and the 1:25,000/1:250,000 MRT geology datasets to delineate boundaries. Thus, 1:25,000 spatial data: “Correct position to within +/- 25m in the final product”. 1:250,000 spatial data. “Generalisations of rock units and fit to 1:250,000 digital topography base gives a final accuracy of up to +/- 250m”. It must be noted that horizontal positional accuracy for well defined features mapped in this dataset may vary widely owing to large differences in the scale of source mapping used in some areas (i.e. where 1:500,000 soil data and 1:25,000 data was used in combination to model ASS areas). Positional accuracy scales are embedded into the dataset attribute table. Attribute Accuracy: Attribution was generally carried out using existing ancillary datasets to assign probability values and in particular classification descriptors. The dataset is therefore dependent on the attribute accuracies of the ancillary datasets employed. Field validation was also carried out to ensure integrity was maintained throughout the final dataset and thus aided in validating the final classification process. Attribute accuracy is estimated to be 90%. Logical Consistency: All polygons, lines and point data labelled. All vertices are snapped and all polygons closed. All data is topologically related. There are no duplicates. Completeness: The dataset covers the entire Tasmania coastal region (except Macquarie Island) between elevations of 0 and 20m AHD. Hence, the data is complete according to the modelling process.