Logical consistency: The shapefile is converted to SDC (Smart Data Compression) format using tools in ArcGIS. The SDC data set is then imported into a file geodatabase to verify, validate, and if needed repair the geometry. Horizontal position accuracy: The data set originally comes from several sources. Most of the data is from U.S. Geological Survey topographic quadrangle maps or sources that exceed its horizontal accuracy. These maps were compiled to meet National Map Accuracy Standards. For horizontal accuracy, this standard is met if at least 90 percent of points tested are within 0.02 inch (at map scale) of their true position. At 1:100,000 scale, 0.02 inch is approximately 167 feet (50.8 meters). Other data details: After processing, the data set is checked for drawing display and number of records and file sizes compared with source materials. Some of the cartographic disparities with this data, inherent in the original 1:100,000 source data, remain in that the density of features can change abruptly. [From National Hydrography Dataset (NHD) documentation - The completeness of the data reflects the content of the sources, which, in the initial release of the National Hydrography Dataset, most often are U.S. Geological Survey topographic maps. Features found on the ground may have been eliminated or generalized on the source graphic because of scale and legibility constraints. In general, streams longer than one mile (approximately 1.6 kilometers) were collected. Most streams that flow from a lake were collected regardless of length. Only definite channels were collected so not all swamp/marsh features have stream/rivers delineated through them. Lake/ponds having an area greater than 6 acres (approximately 2.4 hectares) were collected. Note, however, that these general rules were applied unevenly among maps during compilation. Some map quadrangles have a much sparser pattern of hydrography than do adjoining maps and these differences continue in the digital rendition of these features. Transport reaches are defined on nearly all features of type stream/river, canal/ditch, artificial path, pipeline, and connector. Waterbody reaches are defined on the subset of lake/pond features that were identified as waterbodies during the development of Reach File Version 3. Most attention in applying geographic names was given to transport reaches that follow stream/rivers and waterbody reaches. Near the international boundaries with Canada and Mexico, only the parts of features within the United States are delineated. Detailed capture conditions are provided for every feature type in the Standards for National Hydrography Dataset (USGS, 1999), available online through http://geography.usgs.gov/standards/.]
Notes:
U.S. Rivers and Streams provides a database of linear water features that interconnects and identifies the stream segments or reaches that comprise the surface water drainage system of United States. Largest scale when displaying the data: 1:24,000. Publication date. Vector digital data.
