Important Farmland Maps are compiled by the Farmland Mapping and Monitoring Program (FMMP) pursuant to Section 65570 of the California Government Code. To create the maps, FMMP combines current land use information with U.S. Department of Agriculture-Natural Resources Conservation Service (NRCS) soil survey data. Soil units qualifying for Prime Farmland and Farmland of Statewide Importance are determined by the NRCS. Changes to soil profiles subsequent to publication of NRCS soil surveys are not reflected on this map. This map was developed using NRCS digital soil data (SSURGO) and may contain individual soil units as small as one acre.

Land use status is determined using current and historic aerial imagery and field verification. Principal imagery sources include the U.S. Department of Agriculture National Agricultural Imagery Program, AirPhotoUSA, the High Altitude Missions Branch of NASA, EROS Data Center and SPOT Data Corporation. Additional data on land management and land use conversion activity was made available from the U.S. Fish and Wildlife Service, U.S. Forest Service, California Department of Fish and Game, California Integrated Waste Management Board, and various local government agencies. Map reviewers at the local level contribute valuable information with their comments and suggestions. Cultural base information for the Important Farmland Maps was derived from the U.S. Geological Survey, with updates generated by digitizing over current imagery.