Valleys, featured in the Valley Identification Tool, are locations that have a lower elevation than surrounding areas. EPA Region 1 GIS Center applied ArcGIS' Focal Statistics tool to the USGS 30-meter NED DEM to find places where elevations are significantly less than average. We then quantified population and wood fuel usage within Census County Subdivisions to find locations which may be vulnerable to wood smoke pollution during winter thermal inversions.
Created by US EPA Region 1 GIS Center; and implemented in EPA Regions 2, 3, 9, and 10 by regional GIS staff, US EPA Office of Mission Support (OMS).