Access National Hydrography ProductsThe 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.The NHD is a national framework for assigning reach addresses to water-related entities, such as industrial discharges, 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, much like addresses on streets. 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 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.Statements of attribute accuracy are based on accuracy statements made for U.S. Geological Survey Digital Line Graph (DLG) data, which 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 DLG 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 were validated against a current extract from the Geographic Names Information System (GNIS). The entry and identifier for the names match those in the GNIS. The association of each name to reaches has been interactively checked, however, operator error could in some cases apply a name to a wrong reach.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 close.The completeness of the data reflects the content of the sources, which most often are the published USGS topographic quadrangle and/or the USDA Forest Service Primary Base Series (PBS) map. The USGS topographic quadrangle is usually supplemented by Digital Orthophoto Quadrangles (DOQs). Features found on the ground may have been eliminated or generalized on the source map 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 were collected. Note, however, that these general rules were applied unevenly among maps during compilation. Reach codes are defined on all features of type stream/river, canal/ditch, artificial path, coastline, and connector. Waterbody reach codes are defined on all lake/pond and most reservoir features. Names were applied from the GNIS database. Detailed capture conditions are provided for every feature type in the Standards for National Hydrography Dataset available online through https://prd-wret.s3-us-west-2.amazonaws.com/assets/palladium/production/atoms/files/NHD%201999%20Draft%20Standards%20-%20Capture%20conditions.PDF.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 the true position. Additional offsets to positions may have been introduced where feature density is high 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 as control to assess the positional accuracy of digital data. Digital map elements along the adjoining edges of data sets are aligned if they are within a 0.02 inch tolerance (at map scale). Features with like dimensionality (for example, features that all are delineated with lines), with or without like characteristics, that are within the tolerance are aligned by moving the features equally to a common point. Features outside the tolerance are not moved; instead, a feature of type connector is added to join the features.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.

This resource contains a shapefile of HUC-8 (eight digit Hydrologic Unit Codes) for the Continental United States (CONUS).

The Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the "Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)" “Standard” (http://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit (6th level) for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries are being developed where partners and data exist and will be incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications.

Watersheds in Eaton County, Michigan, USA. These watersheds were created using a hydro-enforced 10ft DEM derived from 2010 Lidar in conjunction with ECGIS hydrology vector layers. The watersheds are simply elevation-based and pay no heed to man-made drainage that may run counter-grade. Delineation occurs confluence to confluence along the flowlines and also around lakes that are 4 hectares or larger.

The Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the "Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)" "Standard" (https://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries are being developed where partners and data exist and will be incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications. For additional information on NHD, go to https://www.usgs.gov/national-hydrography.

The Watershed Boundary Dataset (WBD) defines the areal extent of surface water drainage to a point, accounting for all land and surface areas. Watershed Boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. The intent of defining Hydrologic Units (HU) for the Watershed Boundary Dataset is to establish a base-line drainage boundary framework, accounting for all land and surface areas. At a minimum, the WBD is being delineated and georeferenced to the USGS 1:24,000 scale topographic base map meeting National Map Accuracy Standards (NMAS). Hydrologic units are given a Hydrologic Unit Code (HUC). For example, a hydrologic region has a 2-digit HUC. A HUC describes where the unit is in the country and the level of the unit."A hydrologic unit is a drainage area delineated to nest in a multi-level, hierarchical drainage system. Its boundaries are defined by hydrographic and topographic criteria that delineate an area of land upstream from a specific point on a river, stream or similar surface waters. A hydrologic unit can accept surface water directly from upstream drainage areas, and indirectly from associated surface areas such as remnant, non-contributing, and diversions to form a drainage area with single or multiple outlet points. Hydrologic units are only synonymous with classic watersheds when their boundaries include all the source area contributing surface water to a single defined outlet point."

The MNDNR Watershed Suite is a collection of watershed delineations at various levels, flow network lines, and pour points. This is the newest version updated in 2023. Follow the links below to the individual metadata pages for each layer:

MNDNR Watersheds
MNDNR Level 01 - HUC 02: dnr_watersheds_dnr_level_01_huc_02.html
MNDNR Level 02 - HUC 04: dnr_watersheds_dnr_level_02_huc_04.html
MNDNR Level 04 - HUC 08 - Majors: dnr_watersheds_dnr_level_04_huc_08_majors.html
MNDNR Level 07 - Minors: dnr_watersheds_dnr_level_07_minors.html
MNDNR Level 08 - All Catchments: dnr_watersheds_dnr_level_08_all_catchments.html
MNDNR Level 09 - DNR AutoCatchments: dnr_watersheds_auto_catchments.html

Minnesota Hydrologic Units
Flow Network Lines: dnr_watersheds_catchment_flow_lines.html
Pour Points: dnr_watersheds_catchment_pour_points.html

This data set is a digital hydrologic unit boundary layer that is at the Subwatershed (12-digit) level. The original data set was developed by delineating the boundary lines on base USGS 1:24000 scale topographic quadrangle, and digitizing the delineated lines. Digital Raster Graphics (DRG) images were used for edits to the data layer.This data set consists of geo-referenced digital map data and attribute data. The spatial data are in a statewide coverage format and include complete coverage of the entire state of Connecticut, and small parts of surrounding states. The hydrologic unit ID code attached to each delineated polygon is linked to the attribute data.

The Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the "Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)" “Standard” (http://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit (6th level) for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries are being developed where partners and data exist and will be incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications.

This data set consists of geo-referenced digital data and associated attributes created in accordance with the FGDC Proposal, Version 1.0 - Federal Standards For Delineation of Hydrologic Unit Boundaries 3/01/02 (http://www.nrcs.usda.gov). The hydrologic unit boundaries provide a uniquely identified and uniform method of subdividing large drainage areas. Polygons are attributed with hydrologic unit codes, names, downstream hydrologic unit, flow modifications, and hydrologic unit type for 4th level (8-digit) sub-basin, 5th level (10-digit) watershed, 6th level (12-digit) subwatershed, and acres for subwatershed. An accompanying line shapefile is attributed with the highest hydrologic unit level for each hydrologic unit, linesource, and a metadata reference file.

The Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the "Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)" (https://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries were developed where partners and data existed and were incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications. For additional information on NHD, go to https://www.usgs.gov/national-hydrography.

This dataset is a complete digital hydrologic unit boundary layer to the watershed (10-digit) 6th level at 1:24,000 scale. This data set consists of geo-referenced digital data and associated attributes created in accordance with the FGDC Proposal, Version 1.0 - Federal Standards For Delineation of Hydrologic Unit Boundaries 3/01/02 ( http://www.nrcs.usda.gov/). The hydrologic unit boundaries provide a uniquely identified and uniform method of subdividing large drainage areas. Polygons are attributed with hydrologic unit codes, names, downstream hydrologic unit, flow modifications, and hydrologic unit type for 4th level (8-digit) sub-basin, 5th level (10-digit) watershed, 6th level (12-digit) subwatershed, and acres for subwatershed. An accompanying line shapefile is attributed with the highest hydrologic unit level for each hydrologic unit, linesource, and a metadata reference file.

The United States is divided and sub-divided into successively smaller hydrologic units which are classified into four levels: regions, subregions, accounting units, and cataloging units. The hydrologic units are arranged or nested within each other, from the largest geographic area (regions) to the smallest geographic area (cataloging units). Each hydrologic unit is identified by a unique hydrologic unit code (HUC) consisting of two to eight digits based on the four levels of classification in the hydrologic unit system. The intent of defining Hydrologic Units (HU) within the Watershed Boundary Dataset is to establish a base-line drainage boundary framework, accounting for all land and surface areas. Hydrologic units are intended to be used as a tool for water-resource management and planning activities particularly for site-specific and localized studies requiring a level of detail provided by large-scale map information. The WBD complements the National Hydrography Dataset (NHD) and supports numerous programmatic missions and activities including: watershed management, rehabilitation and enhancement, aquatic species conservation strategies, flood plain management and flood prevention, water-quality initiatives and programs, dam safety programs, fire assessment and management, resource inventory and assessment, water data analysis and water census. The Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the "Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)" "Standard" (http://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit (6th level) for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries are being developed where partners and data exist and will be incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications.View Dataset on the Gateway

The Water Resources Agency and its affiliated agencies provide relevant range information for various river basins for use by government agencies and private organizations, groups, or academic units commissioned by government agencies for specific projects. This dataset is linked to a Keyhole Markup Language (KML) file list, a markup language based on the XML (eXtensible Markup Language) syntax standard, used to express geographic annotations. KML files, written in the KML language, use the XML file format and are applied in Google Earth-related software for displaying geographic data (including points, lines, polygons, models, etc.). Many GIS systems also use this format for exchanging geographic data. The KML data in this dataset uses the UTF-8 encoding.

The Water Resources Agency and its affiliated agencies provide relevant information on the water storage range maps of various reservoirs in Taiwan for use by civil institutions, groups commissioned by government agencies, or academic units for government projects. This dataset is linked to a list of Keyhole Markup Language (KML) files, which is a markup language based on the XML syntax standard. It is developed and maintained by Keyhole, a company owned by Google, for expressing geographical annotations. Documents written in KML language are KML files, which also use the XML file format and are used in Google Earth-related software (Google Earth, Google Map, Google Maps for mobile...) to display geographical data (including points, lines, areas, polygons, polyhedra, and models...). Many GIS-related systems now also adopt this format for exchanging geographical data, with the KML in this dataset using UTF-8 for fields and encoding.

The Watershed and Subwatershed hydrologic unit boundaries provide a uniquely identified and uniform method of subdividing large drainage areas. The smaller sized 6th level sub-watersheds (up to 250,000 acres) are useful for numerous application programs supported by a variety of local, State, and Federal Agencies. This data set is intended to be used as a tool for water-resource management and planning activities, particularly for site-specific and localized studies requiring a level of detail provided by large-scale map information. The dataset will be appended to a larger seamless nationally consistant geospatial database as other states complete their portion of the watershed boundary dataset. Two separate shapefiles were created for downloading purposes. One with arcs (wy_hu12arc.shp) and one with polygons (wy_hu12poly.shp). The same metadata is used for both shapefiles. Only the arc attributes will be found in the wy_hu12arc shapefile. Similarly, only the poly attributes will be found in the wy_hu12poly shapefile.

 This data set is a complete digital hydrologic unit boundary layer to
 the Subwatershed (12-digit) 6th level for the State of Wyoming.This
 data set consists of geo-referenced digital data and associated
 attributes created in accordance with the Federal Standards For
 Delineation of Hydrologic Unit Boundaries 12/06/01
 http://www.sdvc.uwyo.edu/. The data set was
 developed by digitizing watershed boundary lines using 1:24,000
 Enhanced Digital Raster Graphics (DRG-E) geo-referenced topographic
 image base maps and 1:100,000-scale draft boundary lines. The National
 Elevation Dataset (NED) was used to produce the 1:100,000-scale
 preliminary draft boundaries. Polygons are attributed with hydrologic
 unit codes for 4th level sub-basins, 5th level watersheds, 6th level
 subwatersheds, name, size, downsteam hydrologic unit, type of
 watershed, non-contributing areas and flow modification. Arcs are
 attributed with the highest hydrologic unit code for each watershed,
 linesource and a metadata reference file. Two separate shapefiles
 were created for downloading purposes. One with arcs (wy_hu12arc.shp)
 and one with polygons (wy_hu12poly.shp). The same metadata is used for
 both shapefiles. Only the arc attributes will be found in the
 wy_hu12arc shapefile. Similarly, only the poly attributes will be
 found in the wy_hu12poly shapefile.

The Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the "Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)" “Standard” (http://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit (6th level) for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries are being developed where partners and data exist and will be incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications.

(Taken from 11-digit Hydrologic Unit for Alabama abstract, http://www.gsa.state.al.us/gsa/gsa.html

This data set is a digital hydrologic unit boundary that is at the Watershed (11-digit) level for the State of Alabama. The data set was developed by delineating the boundary lines on base maps and digitizing the delineated lines. This data set consists of geo-referenced digital map data and attribute data. The map data, which were captured from 7 1/2 minute quadrangles, comprise a seamless data layer for the entire State of Alabama. All land area within the state can be characterized uniquely as being contained in one and only one hydrologic unit boundary at the 11-digit level. The hydrologic unit ID code attached to each delineated polygon is linked to the attribute data.

The Watershed hydrologic unit boundaries provide a uniquely identified and uniform method of subdividing large drainage areas. These smaller sized hydrologic units (up to 250,000 acres) are useful in many programs supported by federal and state agencies and others. These data are appropriate for use in GIS applications.

All fundamental watershed polygons generated from watershed boundary lines, bank edges, delimiter edges, coastline edges, and administrative boundary edges

The TIGER/Line shapefiles and related database files (.dbf) are an extract of selected geographic and cartographic information from the U.S. Census Bureau's Master Address File / Topologically Integrated Geographic Encoding and Referencing (MAF/TIGER) Database (MTDB). The MTDB represents a seamless national file with no overlaps or gaps between parts, however, each TIGER/Line shapefile is designed to stand alone as an independent data set, or they can be combined to cover the entire nation. Linear Water Features includes single-line drainage water features and artificial path features that run through double-line drainage features such as rivers and streams, and serve as a linear representation of these features. The artificial path features may correspond to those in the USGS National Hydrographic Dataset (NHD). However, in many cases the features do not match NHD equivalent feature and will not carry the NHD metadata codes. These features have a MAF/TIGER Feature Classification Code (MTFCC) beginning with an "H" to indicate the super class of Hydrographic Features.

This dataset is a complete digital hydrologic unit boundary layer to the subwatershed (12-digit) 6th level at 1:24,000 scale. This data set consists of geo-referenced digital data and associated attributes created in accordance with the FGDC Proposal, Version 1.0 - Federal Standards For Delineation of Hydrologic Unit Boundaries 3/01/02. The hydrologic unit boundaries provide a uniquely identified and uniform method of subdividing large drainage areas. Polygons are attributed with hydrologic unit codes, names, downstream hydrologic unit, flow modifications, and hydrologic unit type for 4th level (8-digit) sub-basin, 5th level (10-digit) watershed, 6th level (12-digit) subwatershed, and acres for subwatershed. An accompanying line shapefile is attributed with the highest hydrologic unit level for each hydrologic unit, line source, and a metadata reference file.