EnviroAtlas, EPAThe national component of EnviroAtlas summarizes data for the 48 mainland U.S. states by 12-digit hydrologic unit codes (HUC), of which there are about 90,000 in the United States. Each HUC covers approximately 40 square miles.
The community component of EnviroAtlas summarizes data layers by census block group, providing data at a very fine resolution.