Alaska Geographic Data Committee (AGDC), Unpublished Material, Hydrologic Units for Alaska (fourth level HUC).
This is a Vector data set. It contains the following vector data types (SDTS terminology):
The map projection used is Albers Conical Equal Area.
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 0.001723
Ordinates (y-coordinates) are specified to the nearest 0.001723
Planar coordinates are specified in meters
The horizontal datum used is North American Datum of 1983.
The ellipsoid used is Geodetic Reference System 80.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.257222.
Coordinates defining the features.
Sequential unique whole numbers that are automatically generated.
Coordinates defining the features.
AGDC, EDNA, USGS
The dataset was developed as a statewide effort to produce smaller more manageable watershed units for the state of Alaska. Through an interagency agreement the AGDC has undertaken an effort to produce 4th level hydrologic units following national guidelines.The hydrologic unit boundaries provide a uniquely identified and uniform method of subdividing large drainage areas. These hydrologic units are useful in many programs supported by various agencies. This project is managed by the Bureau of Land Management (BLM).
This data set is intended as a tool for water-resource management and planning activities, particularly for site-specific and localized studies, which require the amount of detail provided by a large-scale map.
U.S. Geological Survey, Unpublished Material, National Hydrography Dataset.
U.S. Geological Survey, Unpublished Material, Catalog Unit Boundaries.
U.S. Geological Survey, Unpublished Material, DRG.
The attributes were proofed by the technicians at the time of input and checked for incorrect or inappropriate data. The attribute format follows the guidelines as prescribed by the Federal Standards For Delineation of Hydrologic Unit Boundaries.
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. The accuracy of these maps is generally based on the contour information or DEM data available for the base maps.
The watershed shapefile was georeferenced to the 1:63360 DRG as required by federal guidelines.The differences in positional accuracy between the hydrologic unit boundaries and their digitized map locations is unknown. Hydrologic unit boundaries generally were digitized within 0.01 inches of their locations on the digitizing source.
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.
The data is based on the National Hydrography Dataset, Digital Elevation Models (60m pixels) and U.S. Geological Survey topographic maps. The completeness of the data reflects the content of the sources. Features found on the ground may have been eliminated or generalized on the source graphics because of scale and legibility constraints.
In the NHD, generally streams longer than one mile (approximately 1.6 kilometers) were collected. Most streams that flow from a lake were collected regardless of their length. Lake/ponds having an area greater than 6 acres approximately 2.4 hectares) were collected. Swamp/marsh features were not 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. Near the international boundary with Canada, only the parts of features within the United States are delineated.
The tests of logical consistency are performed using vendor software.
Are there legal restrictions on access or use of the data?
- Access_Constraints: None
- Acknowledgment of the originating agencies would be appreciated in products derived from these data.
No warranty is made by the Alaska Geographic Data Committee as to the accuracy, reliability, or completeness of these data for individual use or aggregate use with other data. The Alaska Geographic Data Committee is not liable for the misuse of date. Nor is it liable for damage, transmission of viruses, or computer contamination through the distribution of these data sets.
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