Predictive Modeling of Archaeological Sites Lower Adirondack GIS Users Group Meeting September 14, 2005

Why Create a Model? To narrow focus of field investigation to locations most likely to contain prehistoric sites. Contract surveys only test a small sample of total project area Outliers may reveal interesting distinctions between cultures and time periods

Considerations Terrain diversity Resource availability Known sites (i.e., sample pool) Time Period/Cultural Sequence Practical Concerns of Prehistoric Peoples: Food, Water, Shelter, Trade, Protection, Transportation QUESTION: Is all human settlement practical (i.e., cost/benefit analysis)?

Environmental Variables Slope Elevation (absolute, relative) Landforms (valleys, ridgeline…) Aspect (e.g., north-facing) Raw materials (e.g. stone for tools) Water (lakes, streams, confluences) Soil type

Sample Set Accuracy of locations Points versus Polygons Biased pool of known sites Do sites count twice (or more times) if multiple time periods are represented? Is the sample set large enough for statistical accuracy? Narrow set based on time period, culture, site type?

Variables to GIS Data Need measurable GIS data layer to represent each variable Catagorical/Qualitiative coding Raster representation

Model Random Selection of Locations Equal number of known site cells and assumed Non-site cells Logistic Regression Stepwise, backward Eliminate variables with little causality Generate an output GRID Cell value between 0-1 Closer to 0 = low probability of finding sites Closer to 1 = high probability of finding sites

Does the Model Work? Does the final model appear skewed? Test the model in the field

QUESTIONS?