The main Trail Survey took place during the years of 1997-2000. Differentially corrected GPS (Global Positioning System) data were collected primarily on foot for all existing maintained trails and spur trails to backcountry campsites, attractions and buildings within the boundaries of Yellowstone National Park (YNP).The trails that could not be obtained through the GPS or have been rerouted since the survey were acquired through the uses of 1 meter Digital Orthophoto Quarter Quads (DOQQs) and the help of backcountry rangers with knowledge of where the trails are located. There are also associated GPS data for trail bridges, backcountry campsites, patrol cabins and trail surface type. Trail usage data also documented by using visitor ski and bike trail maps. Trails data have been updated since the original survey using information from the Yellowstone Backcountry Office, trails maintenance personnel, best available imagery resources, and GPS data. This layer is a work in progress.