Description: The California Air Districts layer is a polygon shapefile coverage representing the California air pollution control and air quality management districts, as defined in federal and state law. See 40 CFR, Chapter I Section 81, et seq., and California Health and Safety Code, Section 40000 et seq. Shapefile coverage. This data layer shows the air district boundaries and their names as of October 2009. The file has been updated using as main source the: California Environmental Protection Agency Air Resources Board maps (http://www.arb.ca.gov/capcoa/dismap.htm).