Surface Drainage, Field Ditches on Agricultural Land in the Conterminous United States, 1992: National Resource Inventory Conservation Practice 607
This data set represents the estimated percentage of the 1-km grid cell that is covered by or subject to the 
agricultural conservation practice (CP607), Surface Drainage, Field Ditches (SDFD) on agricultural land by 
county.  Surface Drainage, Field Ditches are described as "a graded ditch for collecting excess …