Description: The National Hydrography Dataset (NHD) is a feature-based database that interconnects and uniquely identifies the stream segments or reaches that make up the nation's surface water drainage system. NHD data was originally developed at 1:100,000-scale and exists at that scale for the whole country. This high-resolution NHD, generally developed at 1:24,000/1:12,000 scale, adds detail to the original 1:100,000-scale NHD. (Data for Alaska, Puerto Rico and the Virgin Islands was developed at high-resolution, not 1:100,000 scale.) Local resolution NHD is being developed where partners and data exist. The NHD contains reach codes for networked features, flow direction, names, and centerline representations for areal water bodies. Reaches are also defined on waterbodies and the approximate shorelines of the Great Lakes, the Atlantic and Pacific Oceans and the Gulf of Mexico. The NHD also incorporates the National Spatial Data Infrastructure framework criteria established by the Federal Geographic Data Committee.Selecting Only Major Rivers and Creeks in the NHD using ArcMapfrom the USGS National Hydrography Dataset Newsletter, Vol. 13, No. 8, June 2014, by Jeff Simley, USGSThe NHD contains a lot of information, but for some applications, particularly those at small scales, it needs to be generalized. One approach is to show only “major rivers” in the NHD. A quick technique to show only the named rivers can easily be done by selecting NHDFlowline GNIS_NAME > ‘0’. See: ftp://nhdftp.usgs.gov/Hydro_Images/BlueRiver_Named_Rivers.jpgTo be even more restrictive, major rivers can be defined as only “double-line” or polygonal rivers, which appear in NHDArea. This is more complicated, and takes a few minutes, but works well. This approach finds the Artifical Path of those polygonal rivers:1. Find the polygonal rivers: Select by Attributes NHDArea where FType = 460 - Stream/River.2. Now it is necessary to find the NHDFlowline Artificial Paths of those rivers. Artificial Paths are linked to the polygon they are inside of using the field WBArea_Permanent_Identier. Create the link by doing a relate between NHDFlowline (key WBArea_Permanent_Identifier) and NHDArea (key Permanent_Identifier)3. Invoke the relationship and select the corresponding NHDFlowlines.4. For clarity, turn off the NHDArea selected features (the polygonal rivers).5. Now the candidate artificial paths are selected, but there are two problems: One is that the rivers running through lakes are not selected (which they should be), and two, the “stubs”of the tributary artificial paths have been selected (which are not wanted). 6. Next order of business is to eliminate the minor stubs with no name. Select from selection by Attributes NHDFlowline GNIS_Name > ‘0’. Now only stubs that are named remain. 7. Some of the remaining candidate artificial paths are wanted (the major rivers) and some are not (the named stubs). The named stubs can be eliminated by virtue of the fact that there are very few of them (normally one record per name) and those with low counts can be eliminated.8. Open the NHDFlowline attribute table. Some records are selected (the remaining candidate list) and some are not (all other flowlines making up “minor rivers”). Summarize the number of records under the field GNIS_Name and write this out as Sum_Output.dbf which you then add to ArcMap.9. Now the goal is to find the names of the major rivers. These will be rivers with a record count greater than 1. The extraneous non-named stubs have already been eliminated, which helps reduce the load. The next steps will select only records with significant counts, that is, the major rivers. This will allow deselecting the remaining NHDFlowlines and in the process eliminate the named stubs.10. It is necessary to relate Sum_Output (key GNIS_Name) with NHDFlowline (key GNIS_Name) to make it possible to use the GNIS_NAME’s to select the major rivers in NHDFlowline.11. Open the Sum_Output table. Note the field Count_GNIS_Name which will be used to count records. This will eliminate named stubs, leaving just the major rivers selected. Create a New Selection, Cnt_GNIS_N > 1. Leave the table open. Note major rivers are selected.Invoke the relationship to select the major rivers. In ArcMap all “major rivers” have been selected, even rivers through lakes. See ftp://nhdftp.usgs.gov/Hydro_Images/Blue_River_Selected.jpg