Surface Drainage-Main or Lateral on Agricultural Land in the Conterminous United States, 1992: National Resource Inventory Conservation Practice 608
This data set represents the estimated percentage of the 1-km grid cell that is covered by or subject to the 
agricultural conservation practice (CP608), Surface Drainage, Main or Laterals (SDML) on agricultural land 
by county. Surface Drainage, Main or Laterals are described as "an open drainage ditch constructed to …