What is the positional accuracy of the NHD?
Original hydrographic data were compiled to meet National Map Accuracy standards. These standards have been maintained in the process of creating the NHD. At 1:100,000 scale, ninety percent of well-defined features are within 167 feet (0.02 inches at map scale) of their true geographic position. When higher resolution data are created and submitted, the positional accuracy may vary due to processing procedures of the contributing sources. USGS Map Accuracy standards for 1:24,000 scale require ninety percent of well-defined features to lie within 40 feet of their true geographic position. What sources were used to produce the data? It’s a combination of USGS hydrologic digital line graph files and EPA reach files, version 3.0 (RF3). The USGS files are used for spatial accuracy and the EPA files are used for attribute information. Why has this dataset been created? The idea is to combine spatial accuracy with detailed features, attributes, and values. Information such as flow paths, perm
