The California Department of Water Resources appraises statewide water demands by performing land use surveys by county or other study area on a rotating basis. Central District surveys its counties every seven to ten years, depending upon the changes in land use for that county. The objective of these land and water use studies is the appraisal of water demands for beneficial purposes and the assessment of water supplies to satisfy those demands. A secondary objective is to analyze the present and potential water needs of the area being studied. The land use portion of the study maps the entire county, identifying agriculture (irrigated and non-irrigated), urban, and developed recreation areas; using as many as 200 separate classes. Irrigated acreage is mapped by specific land use type, and often includes mapping the water source by surface, groundwater or mixed source when known. These surveys and assessments are also used for statewide planning purposes. Some previous studies evaluated land and water resources by hydrologic boundaries that oftentimes cover more than one county or parts of counties.