The Internet Archive discovers and captures web pages through many different web crawls.
At any given time several distinct crawls are running, some for months, and some every day or longer.
View the web archive through the Wayback Machine.
Elevation Derivatives for National Applications (EDNA)
EDNA is a multi-layered database derived from a version of the National Elevation Dataset (NED), which has been hydrologically conditioned for improved hydrologic flow representation. The seamless EDNA database provides 30 meters resolution raster and vector data layers including:
Reach Catchment Seedpoints
Hydrologically conditioned elevation data, systematically and consistently processed to create hydrologic derivatives,can be useful in many topologically based visualization and investigative applications. Drainage areas upstream or downstream from any location can be accurately traced facilitating flood analysis investigations, pollution studies, and hydroelectric power generation projects.
Additional information about the Elevation Derivatives for National Applications (EDNA) database is available online at https://lta.cr.usgs.gov/edna.