The U.S. Fish and Wildlife Service (FWS) has been conducting a nationwide survey of wetlands and deepwater habitats since the mid-1970s through its National Wetlands Inventory Program (NWI). This survey is accomplished using traditional photointerpretation techniques to produces map and digital geospatial data on the status of wetlands. The U.S. Geological Survey topographic maps serve as the base data upon which boundaries of wetlands and deepwater habitats are delineated.