For more than a decade the USGS Gap Analysis Program has focused considerable effort on mapping land cover to assist in the modeling of wildlife habitat and biodiversity for large geographic areas. The GAP Analysis Program has been traditionally state-centered; each state having the responsibility of implementing a project design for the geographic area within their state boundaries. The Southwest Regional Gap Analysis Project (SWReGAP) was the first formal GAP project designed at a regional, multi-state scale. The project area comprises the southwestern states of Arizona, Colorado, Nevada, New Mexico and Utah, and involved the collaborative efforts of many individuals from institutions within each of the five states. Project duration lasted approximately 5 years, beginning in 1999 and ending in 2004. The land cover map was generated using regionally consistent geospatial data (Landsat ETM+ imagery and DEM derivatives), similar field data collection protocols, a standardized land cover legend, and a common modeling approach (decision tree classifier).
Partitioning of mapping responsibilities amongst the 5 collaborating states was organized around ecoregion based “mapping zones.” Over the course of three field seasons approximately 93,000 field samples were collected to train the land cover modeling effort. Land cover modeling was done using a decision tree classifier.