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This data represents a land use survey of Butte County conducted by DWR, Northern District Office staff, under the leadership of Tito Cervantes, Senior Land and Water Use Supervisor. The field work for this survey was conducted during the summer of 2004. ND staff physically visited each delineated field, noting the crops grown at each location. Field survey boundary data was developed using: 1. The aerial photography used for this survey was taken in June of 2004. 9”x9” color photographs were generated from an altitude of about 6,000 feet above ground to produce a 1:24,000 scale photo. 2. The 9”x9” photos were taken to the field and virtually all the areas were visited to positively identify the land use. Site visits occurred July through September 2004. Land use codes were hand written on the photos. 3. Using AUTOCAD, the land use boundaries were digitized from USGS Digital Orthophoto Quarter Quadrangles (DOQQs) and attributes were entered from the field photos (using a standardized digitizing process). 4. After quality control/assurance procedures were completed on each file (DWG), the data was finalized. 5. The linework and attributes from each DWG quad file were brought into ARCINFO and both quad and survey wide coverages were created, and underwent quality checks. The survey wide coverage was then converted to a shapefile using ARCVIEW. The primary focus of this land use survey is mapping agricultural fields. Urban residences and other urban areas were delineated using aerial photo interpretation. Some urban areas may have been missed, especially in forested areas. Before final processing, standard quality control procedures were performed jointly by staff at DWR's Northern District, and at DPLA headquarters under the leadership of Jean Woods, Senior Land and Water Use Supervisor. After quality control procedures were completed, the data was finalized. The positional accuracy of the digital line work, which is based upon the 9' x 9' color photos, is approximately 23 meters. The land use attribute accuracy for agricultural fields is high, because almost every delineated field was visited by a surveyor. The accuracy is 95 percent because some errors may have occurred. Possible sources of attribute errors are: a) Human error in the identification of crop types, b) Data entry errors. |