Learn more about EPA Level III and Level IV ecoregions
Ecoregions are areas similar in type, quality, and quantity of environmental resources. They are identified through the analysis of patterns of biotic and abiotic phenomena, including geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology. The relative importance of each characteristic varies from one ecological region to another. A Roman numeral hierarchical scheme has been adopted for different levels for ecological regions. Level III and IV are the most useful resolutions of ecoregion data. At Level III, the continental United States contains 105 regions. Level IV ecoregions are further subdivisions of Level III ecoregions.
Descriptions of Level III and IV ecoregions by state are available here.
Ecoregions are available in Transect under Setting > Ecoregions.