The CHAT data roll up.

The states working with the Western Governors Association to develop the Crucial Habitat Assessment Tool (CHAT) identified a suite of common variables to model areas of crucial habitat to create a consistent representation of crucial habitats across the western United States for the CHAT.  By first defining common input variables to create either a state by state or region-wide data layer, it then became each state’s responsibility to determine how each of those variables would be used to identify areas of crucial habitat.  This crucial habitat “roll-up” used one of two general methodologies to define crucial areas.  The first method was an empirical model that statistically identified the most crucial areas.  The second approach was a categorical model in which state biologists identified key variables and thresholds to define the various levels of crucial habitat.  We provide examples of each method and different crucial habitats as well as reasons one method was chosen over another.  Each state’s final product was a hexagon layer with attribute scores of 1-6 for each of the variables and final crucial habitat score.  These were then  joined by hexagon ID to create a west-wide hexagon layer.  Discrepancies along state borders reflect the independence of states to define their own crucial habitats while still creating a west wide CHAT layer.  We discuss the CHAT in terms of representation of state policies/priorities for conservation and their use to planners and for project evaluations prior to decisions for locating routes or locations of projects.