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National Hydrography Dataset


Note to Users: Metadata for each specific subbasin and quadrangle will need to be accessed. The following is a general NHD metafile. 


      U.S. Geological Survey in cooperation with U.S. Environmental Protection Agency


      National Hydrography Dataset

Publication Place:

      Reston, Virginia

Publication Date:



      U.S. Geological Survey


      The National Hydrography Dataset (NHD) is a feature-based database that

      interconnects and uniquely identifies the stream segments or reaches that

      comprise the nations surface water drainage system. It is based initially on

      the content of the U.S. Geological Survey 1:100,000-scale Digital Line Graph

      (DLG) hydrography data, integrated with reach-related information from the U.S.

      Environmental Protection Agency Reach File Version 3.0 (RF3). More

      specifically, it contains reach codes for networked features and isolated

      lakes, flow direction, names, stream level, and centerline representations for

      areal water bodies. Reaches are also defined to represent 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 set out by the Federal Geographic Data



      The National Hydrography Dataset combines elements of the DLG and RF3: spatial

      accuracy and comprehensiveness from the DLG and network relationships, names,

      stream level, and a unique identifier (reach code) for surface water features

      from RF3. The NHD supersedes DLG and RF3 by incorporating them, not by

      replacing them. Users of DLG and RF3 will find the National Hydrography Dataset

      both familiar and greatly expanded and refined. The NHD provides a national

      framework for assigning reach addresses to water-related entities, such as

      industrial dischargers, drinking water supplies, fish habitat areas, wild and

      scenic rivers. Reach addresses establish the locations of these entities

      relative to one another within the NHD surface water drainage network in a

      manner similar to street addresses. Once linked to the NHD by their reach

      addresses, the upstream/downstream relationships of these water-related

      entities and any associated information about them can be analyzed using

      software tools ranging from spreadsheets to geographic information systems

      (GIS). GIS can also be used to combine NHD-based network analysis with other

      data layers, such as soils, land use and population, to help better understand

      and display their respective effects upon one another. Furthermore, because the

      NHD provides a nationally consistent framework for addressing and analysis,

      water-related information linked to reach addresses by one organization

      (national, state, local) can be shared with other organizations and easily

      integrated into many different types of applications to the benefit of all. The

      National Hydrography Dataset is designed to provide comprehensive coverage of

      hydrologic data for the U.S. While initially based on 1:100,000-scale data, the

      NHD is designed to incorporate - and encourage the development of -

      higher-resolution data required by many users. It will facilitate the improved

      integration of water-related data in support of the application requirements of

      a growing national user community and will enable shared maintenance and




Maintenance and Update Frequency:


Theme Keyword Thesaurus:

      U.S. Department of the Interior, U.S. Geological Survey, 1997, Standards for

      National Hydrography Dataset(

      Theme Keyword:


      Theme Keyword:

            Stream / River

      Theme Keyword:

            Lake / Pond

      Theme Keyword:

            Canal / Ditch

      Theme Keyword:


      Theme Keyword:

            Spring / Seep

      Theme Keyword:

            Swamp / Marsh

      Theme Keyword:

            Artificial Path

      Theme Keyword:


Access Constraints:


Use Constraints:

      None. Acknowledgment of the originating agencies would be appreciated in

      products derived from these data.

Attribute Accuracy Report:

      The accuracy of the attributes of the Digital Line Graph data is estimated to be

      98.5 percent. One or more of the following methods were used to test attribute

      accuracy: - manual comparison of the source with hardcopy plots. - symbolized

      display of the digital line graph on an interactive computer graphic system. -

      Selected attributes that could not be visually verified on plots or on screen

      were interactively queried and verified on screen. In addition, software

      validated feature types and characteristics against a master set of types and

      characteristics, checked that combinations of types and characteristics were

      valid, and that types and characteristics were valid for the delineation of the

      feature. Feature types, characteristics, and other attributes conform to the

      Standards for National Hydrography Dataset (USGS, 1999) as of the date they

      were loaded into the database. All names on reaches were validated against a

      March 1999 extract from the Geographic Names Information System. The entry and

      identifier for the names match those in the Geographic Names Information

      System. The association of each name to reaches has not been methodically

      checked, and so a name may be applied to the wrong reaches. Anecdotal reviews

      indicate that 80 percent or more of the named reaches have the correct name.

      Reaches were delineated with a batch procedure and were checked extensively

      during the visual pass steps of processing. Based on automated quality

      assurance/quality control checks performed at various intervals during the

      processing, approximately 99 percent of the reaches are delineated according to


Logical Consistency Report:

      Points, nodes, lines, and areas conform to topological rules. Lines intersect

      only at nodes, and all nodes anchor the ends of lines. Lines do not overshoot

      or undershoot other lines where they are supposed to meet. There are no

      duplicate lines. Lines bound areas and lines identify the areas to the left and

      right of the lines. Gaps and overlaps among areas do not exist. All areas


Completeness Report:

      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 their 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. A priority for maintenance of the National

      Hydrography Dataset is the rectification of these differences. 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

Horizontal Positional Accuracy Report:

      Statements of horizontal positional accuracy are based on accuracy statements

      made for U.S.Geological Survey topographic quadrangle maps. 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. Additional offsets to positions may have

      been introduced where there are many features to improve the legibility of map

      symbols. In addition, the digitizing of maps is estimated to contain a

      horizontal positional error of less than or equal to 0.003 inch standard error

      (at map scale) in the two component directions relative to the source maps.

      Visual comparison between the map graphic (including digital scans of the

      graphic), and plots or digital displays of points, lines, and areas, is used to

      assess the positional accuracy of digital data. Linear features of the same

      type along the adjoining edges of data sets are aligned if they are within a

      0.02 inch tolerance (at map scale). To align the features, the midpoint between

      the end of the corresponding features is computed, and the ends of features are

      moved to this point. Features outside the tolerance are not moved; instead, a

      feature of type connector was added to join the features.

Vertical Positional Accuracy Report:

      Statements of vertical positional accuracy for elevation of water surfaces are

      based on accuracy statements made for U.S. Geological Survey topographic

      quadrangle maps. These maps were compiled to meet National Map Accuracy

      Standards. For vertical accuracy, this standard is met if at least 90 percent

      of well-defined points tested are within one-half contour interval of the

      correct value. Elevations of water surface printed on the published map meet

      this standard; the contour intervals of the maps vary. These elevations were

      transcribed into the digital data; the accuracy of this transcription was

      checked by visual comparison between the data and the map.

Direct Spatial Reference Method:


Latitude Resolution:


Longitude Resolution:


Geographic Coordinate Units:

      Decimal Degrees

Horizontal Datum Name:

      North American Datum of 1983

Ellipsoid Name:

      Geodetic Reference System 80

Semi-major Axis:


Denominator of Flattening Ratio:


Altitude Datum Name:

      National Geodetic Vertical Datum of 1929

Altitude Resolution (Primary):


Altitude Distance Units:


Altitude Encoding Method:

      Attribute Values

Entity and Attribute Overview:

      The National Hydrography Dataset is a comprehensive set of digital spatial data

      that encodes information about naturally occurring and constructed bodies of

      water, paths through which water flows, and related entities. The information

      encoded about features includes classification by type, other characteristics,

      a unique common identifier, the feature length or area, and (rarely) the

      elevation of the surface of water pools and a description of the stage of the

      elevation. For reaches, encoded information includes a reach code, the date the

      reach code was assigned, a unique common identifier, the reach length or area,

      and, for transport reaches, the stream level. Geographic names, and their

      identifiers in the Geographic Names Information System, are assigned to reaches

      or, if no reach is available, to features. The data also contain relations

      among reaches that encode the direction of water flow, metadata, and

      information that supports the exchange of future updates and improvements to

      the data.

Entity and Attribute Detail Citation:

      The names and definitions of all feature types, characteristics, and values are

      in U.S. Geological Survey, 1999, Standards for National Hydrography Dataset:

      Reston, Virginia, U.S.Geological Survey. The document is available online

      through Information about tables and fields

      in the data are available from the user documentation for the National

      Hydrography Dataset.

Metadata Date:


Metadata Standard Name:

      FGDC Content Standards for Digital Geospatial Metadata

Metadata Standard Version: