Other Research Sites: Research Sites: This map layer is a combination of three data sets: location of core NEON sites, NADP sites, and Biological Field Stations. State and Province Boundaries: and Province Boundaries: This map layer show outlines of Mexican States, Canadian Providences, and the 48 contiguous states. US States Only: States Only: This map layer contains shows outlines of the 48 contiguous states only. Regional Watersheds Outline: Watersheds Outline: This map layer contains hydrologic unit boundaries and codes for the United States. It was revised for inclusion in the National Atlas of the United States of America, and updated to match the streams file created by the USGS National Mapping Division (NMD) for the National Atlas of the United States of America. This is a revised version of the November 2002 map layer. Citation: National Atlas of the United States. Subregional Watersheds Outline: Watersheds Outline: This map layer contains hydrologic unit boundaries and codes for the United States. It was revised for inclusion in the National Atlas of the United States of America, and updated to match the streams file created by the USGS National Mapping Division (NMD) for the National Atlas of the United States of America. This is a revised version of the November 2002 map layer. Citation: National Atlas of the United States. US Rivers Major: Rivers Major: This map layer shows major rivers of the United States. US Rivers Minor: Rivers Minor: This map layer shows areal and linear water features of the United States. The original file was produced by joining the individual State hydrography layers from the 1:2,000,000- scale Digital Line Graph (DLG) data produced by the USGS. This map layer was formerly distributed as Hydrography Features of the United States. This is a revised version of the January 2003 map layer. Citation: National Atlas of the United States. Bailey’s Ecoregions by Division: Ecoregions by Division: This map layer is commonly called Bailey’s ecoregions and shows ecosystems of regional extent in the United States. Four levels of detail are included to show a hierarchy of ecosystems. The largest ecosystems are domains, which are groups of related climates and which are differentiated based on precipitation and temperature. Divisions represent the climates within domains and are differentiated based on precipitation levels and patterns as well as temperature. Also identified are mountainous areas that exhibit different ecological zones based on elevation. Citation: National Atlas of the United States. Bailey’s Ecoregions by Providence: Ecoregions by Providence: This map layer is commonly called Bailey’s ecoregions and shows ecosystems of regional extent in the United States. Four levels of detail are included to show a hierarchy of ecosystems. The largest ecosystems are domains, which are groups of related climates and which are differentiated based on precipitation and temperature. Divisions represent the climates within domains and are differentiated based on precipitation levels and patterns as well as temperature. Divisions are subdivided into provinces, which are differentiated based on vegetation or other natural land covers. Also identified are mountainous