The United States Geological Survey (USGS) and National Park Service (NPS) formed the USGS-NPS Vegetation Mapping Program in 1994 to map the vegetation of National Park System units in accordance with the updated U.S. National Vegetation Classification (USNVC). In 1996, the Vegetation Inventory and Type Mapping Project of Yosemite National Park was initiated as a pilot project to assess how well existing data could be integrated in the classification. Aerial Information Systems, Inc. (AIS) was subcontracted by the primary contractor, Environmental Research Institute (ESRI), to form a team that would perform photinterpretation, data integration, preliminary classification, field data collection, and accuracy assessment. Nature Serve and Yosemite National Park staff established study area boundaries. The mapping study area, consists of approximately 1,387,451 acres of Yosemite National Park and Devils Postpile National Monument as identified by Yosemite staff. Work was performed on the project between 1997 and 2003. In 1997, a preliminary vegetation classification was developed by Nature Serve/California State Heritage Program and USGS staff using existing datasets and a gradsect analysis was made to allocate field sampling points within the study area. These pre-existing data included the Weislander Data of 1935-1937, Natural Resources Inventory (NRI) Data of 1988-1993, and U.S Forest Service Upland and Riparian Classification Plots analysis by Don Potter in 1994 and 1998. The grandsect analysis entailed establishing the environmental variables most influential on Yosemite's vegetative diversity and then producing a spatial model of predicted vegetative diversity based on the environmental variables. A grid of plots known as Biophysical Units (BPUs) was then created. Unsampled BPUs were selected for field data collection with a focus on those which needed sampling for Yosemite's overall classification scheme and those which presented undefined signatures to photointerpreters. In Spring 1998, NatureServe ecologists developed a releve-based standardized field data collection protocol. Between the 1998 and 199 field seasons, Nature Serve staff sampled a total of 604 plots at the times when each plot's flowering phenology reached optimal sampling conditions and the most species would be identifiable. AIS photointerpreters jointly conducted field reconnaissance with USGS and NatureServe ecologists during the 199 field season and provided photo delineations of unsampled BPUs. Photointerpretation for the finalized map was completed by AIS between 2000 and 2002. CNPS under separate contract and in collaboration with CDFW VegCAMP developed the floristic vegetation classification used for the project. The floristic classification follows protocols compliant with the Federal Geographic Data Committee (FGDC) and National Vegetation Classification Standards (NVCS). Aerial imagery was collected in 1997 at a scale of 1: 5,860 to be interpreted for vegetation cover and serve as the base for attribute coding, both of which tasks were done by AIS. Each aerial photo was prepared with 23 cm x 23 cm frosted mylar overlay. Digital orthophoto quarter quadrangles (DOQQs) from 1987-1999 (black-and-white and infra-red) were used in combination with aerial imagery to identify control points. Mono Digitizing Stereo Digitizing (MDSD, Carto Instruments Incorporated, Seattle, WA) software used the control points and NatureServe's vegetation linework for data automation, automatically georeferencing each photo to the DOQQ with real-world coordinates. Digitized linework was then converted from MDSD outfile format to a coverage using ARC/INFO (Environmental Systems Research Institute, Inc., Redlands, CA).