Aboriginal site features occur across the entire landscape; however, some parts of the landscape have a greater capacity to contain certain site features or features of different types. The variation in site feature likelihood across the landscape is useful for planning assessments of potential site impacts.
The ASDST has been developed to support the assessment Aboriginal sites issues in NSW at the landscape-scale. The tool extends the Aboriginal Heritage Information Management System (AHIMS) by illustrating the potential distribution of site features recorded in the database.
Site predictive models
The maps of site feature predictions made by the Aboriginal Sites Decision Support Tool (ASDST) are based on the application of site predictive modelling. This is a technique used to correlate site information in AHIMS with landscape patterns such as proximity to water, vegetation, terrain, soils and so on.
The maps provide a regional overview about site feature distribution and related issues about the level of accumulated impacts they have experienced, where data gaps in the AHIMS data base remain, and where these gaps can be addressed through further survey.
To download the ASDST models, go to the SEED website and use the term 'ASDST' in search criteria.
How can they be used?
The mapping tool provides interactive access to the maps generated by the ASDST and can be used as a way of visualising site feature potential and related issues across the whole landscape.
The ASDST Product Outline Technical Summary (PDF 5MB) is a document describing the appropriate interpretation of the ASDST products, their application in regional-scale projects and a technical explanation of how they were derived. Users are encouraged to read this document in order to interpret the ASDST products appropriately and understand how they were derived.
Limitations
The products have been developed to meet the needs of regional planning. For this reason, they are designed to be used at scales of 1:100,000 and above. Application at finer scales is possible, but it should be borne in mind that the datasets used to derive the products were themselves derived at a scale of 1:100,000 or coarser, and therefore the inaccuracies of those layers at finer scales will be carried through to the ASDST products.
It is intended that all products will develop over time. They will be periodically reviewed as new data becomes available, parameters are assessed, models are progressively better validated and modelling approaches are refined. For this reason, all products have a version number attached and, for any analysis, mapping or reporting that is performed from the layers, the version that was used should be specified. The current version of all products is version 7.
Contact us
For further information and support in interpreting the ASDST products, email [email protected].
The ASDST is composed of an integrated suite of spatial GIS layers. The collection of GIS layers are organised around the following products:
- Pre1750 (original) models.
- Current models
- Combined accumulated impacts
- Combined model reliability
- Combined survey priority.
The pre1750 (1) and current models (2) products are comprised of 10 raster (grid) GIS layers, each representing different feature types. Splitting the products into feature types permits the landscape distribution and nature of impacts of each feature to be modelled separately, leading to a more specific product. The last 3 products are single grid layers, which are derivatives of the Pre1750 and current products.
The following layers form the pre1750 and current model suites:
- All feature types combined (ALL)
- Stone artefacts (AFT)
- Rock art (ART)
- Burials (BUR)
- Western earth mounds and shell (ETM)
- Grinding grooves (GDG)
- Hearths (HTH)
- Coastal shell middens (SHL)
- Stone quarries (STQ)
- Scarred trees (TRE).
For each product (and individual feature products) is a raster GIS layer. Raster GIS layers describe a feature that varies continuously over a landscape and is represented by cells (like pixels in a digital photograph) that represent a part of the landscape as a square. The square in the ASDST products represents 1 Ha on the landscape. Raster GIS layers are different to GIS shapefiles that represent features on a landscape as points, lines or polygons. Raster GIS layers have a regularly spaced arrangement of cells that cover the whole landscape. Each cell is attributed with a value indicating the relative value of what the layer is describing at that place. For the ASDST products, this may be the relative likelihood of a site feature, relative survey priority or the relative reliability of the model.
The pre1750 models are a set of raster GIS layers describing the relative likelihood of Aboriginal site features occurring across the landscape. They have been derived using AHIMS data, and a set of spatial variables describing the landscape as it is estimated to have been prior to European settlement.
The pre1750 models do not take into account the level of destruction of sites in the intervening period (for instance, from agriculture, mining or urbanisation), nor the detectability of different site features (that is, whether locating them would require excavation), or local conditions that may lead to the lack of a feature being preserved. They are therefore not meant to convey a likelihood profile of the present landscape or how easily sites could be located. When interpreting the pre1750 models, the level of impact in the current landscape should be evaluated by comparing them to the corresponding current extent models.
The pre1750 models describe the relative likelihood of finding a particular type of Aboriginal site feature asit is assumed to have been in the pre1750 landscape (for example, scarred tree or stone artefact). They are therefore a baseline for site potential in the landscape. The legend for each layer is scaled from white (low likelihood) to black (high likelihood). When looking at any pre1750 layer, the darker it is, the higher the likelihood that that feature could be located there 200 years ago, according to the predictions made by the model.
It is important to keep in mind when looking at how dark an area of the model is, that the darkness is a relative quality. Black does not guarantee that that feature would have been located there or would still be there today. It represents an area where the model predicts that the likelihood of that feature at that location is high relative to all other areas of the landscape. Similarly, white areas do not indicate an absolute absence of that feature, but the lowest relative likelihood that was resolved by the model.
The models are not calibrated to the absolute probability of presence or absence of site features, but instead describe relative likelihood as it changes over the landscape.
The relative nature of the likelihood values of each model also extends to what each cell value’s likelihood is measured relative to. When looking at any of the models, it should be kept in mind that relative likelihood is relative to the entire extent of the layer. Thus:
The likelihood at any given cell is relative to all other cells in the layer (that is, the rest of New South Wales).
A further complication with the relative nature of the likelihood measure is that it is not directly comparable between site features. So, for instance, although one area might indicate high modelled likelihood for both stone quarries and artefacts, that does not mean they are both predicted to have an equal probability of occurrence. In this example, the absolute probability of locating quarries is still less because they are generally less frequently observed than stone artefacts. Thus:
The relative likelihood between different site features is not directly comparable in absolute probability terms.
The current models are modifications of the pre1750 models so that they reflect a more realistic likelihood of site features occurring in the present-day landscape. These layers do this by utilising tenure, native vegetation extent, land-use mapping and mining history (for example, sand mining) to place parameters upon the likely survival rates of different features under different types of land-use and land condition. Parameters estimating impacts were derived through consultation and a series of expert workshops. Tenure and tenure history was used to provide an idea for how long:
- parts of the landscape have been managed for conservation (for example, as a national park)
- native vegetation extent was used to identify those areas of the landscape that have been subjected to clearing
- land-use mapping indicates how land is currently used (that is, cropping, grazing, roads or urban)
- mining reveals which parts of the landscape where site likelihood has been irretrievably degraded (for example, even though it might now be in a national park and covered in native vegetation).
The current models take into account estimated historical impacts on Aboriginal features to describe their potential occurrence in the present-day landscape.
The caveats described in the previous section for interpreting likelihood for the pre1750 layers also apply to interpreting the current models (ie their scale is approximately 1:100,00). However, the relative likelihood in the current models takes into account the relative chance of a feature to survive under different land-use conditions in the landscape.
It does this by reducing the pre1750 likelihood values using the level of impact a land-use probably had on a feature. So, for example, a cleared landscape would be expected to reduce the likelihood of scarred trees to almost zero; whereas the likelihood of stone artefacts surviving in the same la