The National Ecological Observatory Network includes 81 field sites across 20 ecoclimatic Domainsthat cover the contiguous 48 U.S. states, Alaska, Hawaii, and Puerto Rico. Each Domain represents a distinct region of vegetation, landforms, climate, and ecosystem performance. Domain boundaries were determined using a statistical clustering algorithm and data developed by William Hargrove and Forrest Hoffman of the Oak Ridge National Laboratory. Site locations were chosen for a variety of reasons, including scientific criteria and permitting logistics. NEON is a national Observatory, not a collection of regional observatories. Data are collected at field sites and sent to a headquarters location in Boulder, Colorado. Data are processed and then made available via the internet. NEON also has 18 field offices (Domain support facilities) staffed by field scientists who manage the observational data collection and instrumentation at field sites.