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1971. United States. Bureau of Transportation Statistics and Stackhouse, Cecil. This polygon shapefile depicts nonattainment and maintenance areas for the United States and its Territories for the enforcement of the sulfur diox... United States. Bureau of Transportation Statistics.
1978. United States. Bureau of Transportation Statistics and Stackhouse, Cecil. This polygon shapefile depicts nonattainment and maintenance areas for the United States and its Territories for the enforcement of the sulfur diox... United States. Bureau of Transportation Statistics.
2010. United States. Bureau of Transportation Statistics and Stackhouse, Cecil. This polygon shapefile depicts nonattainment and maintenance areas for the United States and its Territories for the enforcement of the sulfur diox... United States. Bureau of Transportation Statistics.