Datasets created for the Border Environmental Health Initiative (BEHI) follow watershed boundaries as defined by Woodward and Durall (1996). As part of the U.S.-Mexico Border Field Coordinating Committee Issues Team, Woodward and Durall used surface-water drainage basins as the primary basis for defining and delineating the extent of the border area from a shared-water resources perspective. In order to provide integrated datasets in the border region, local and regional BEHI datasets have been clipped to this boundary. A map of this extent can be found at: <http://borderhealth.cr.usgs.gov>.
The polygon feature class is a synthesis of USGS HUC boundaries and SEMARNAT 1:250k cuenca boundaries. The international boundary digitized from 2004 DOQQs as a part of the USGS Border Environmental Health Initiative was used to provide a common boundary for the U.S. and Mexico watersheds. This feature class forms the basis for the study area boundary with 8 sub-areas for the USGS U.S.-Mexico Border Environmental Health Initiative. Sources included the 250k 8-digit HUCs from the USGS Water Resources NSDI Node (<http://water.usgs.gov/lookup/getgislist>) and 1:250k watershed boundaries from Mexico's Instituto Nacional de Estadística, Geografía, e Informatica (<http://www.inegi.gob.mx>).