The Forest Vegetation Simulator (FVS) is the USDA Forest Service's nationally supported framework for forest growth and yield modeling. A 'variant' is a model calibrated to a specific geographic area. Within each variant, location codes are used to adjust model parameters and determine volume equations. In most variants, location codes are assigned as a standardized code that identifies a national forest or a specific district, but there are a few exceptions. In this GIS layer most FVS location codes have been assigned based on the proclaimed forest boundaries (not administrative boundaries). Areas outside of national forest boundaries have been assigned location codes based on proximity and similarity to national forest lands. There has been exactly one variant and one location code assigned for every location within the United States. Each polygon represents the location code that could be used as the default based on geographic location alone. This layer is not intended to identify the only variant and location code, nor even the best for any particular location, and a user of the FVS model is free to select whatever variant and location code they feel is appropriate for their data. Please refer to the FVS documentation (Variant Overviews) for a description of the geographic extent of the data used to develop each variant.