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Hydrologic Units Map of Wyoming, Modified from USGS Fourth Level Units


Steeves, Peter and Douglas Nebert; modified by Tom Kohley, Wyoming Water Resources Center
Publication_Date: 19948
Hydrologic units map of Wyoming, modified from USGS fourth level units
Publication_Place: Reston, Virginia; Laramie, Wyoming
U.S. Geological Survey; University of Wyoming Spatial Data and Visualization Center
Online_Linkage: <URL:>
The Geographic Information Retrieval and Analysis System (GIRAS) was developed in the mid 70s to put into digital form a number of data layers which were of interest to the USGS. One of these data layers was the Hydrologic Units. The map is based on the Hydrologic Unit Maps published by the U.S. Geological Survey Office of Water Data Coordination, together with the list descriptions and name of region, subregion, accounting units, and cataloging unit. The hydrologic units are encoded with an eight- digit number that indicates the hydrologic region (first two digits), hydrologic subregion (second two digits), accounting unit (third two digits), and cataloging unit (fourth two digits).

The data produced by GIRAS was originally collected at a scale of 1:250,000.

This data set is a modification for Wyoming of the original United States HUC data produced by the USGS. The primary modifications made in this data set by the Wyoming Water Resources Center include 1) removal of hydrologic units that do not drain within Wyoming and 2) modification of the hydrologic unit boundaries to better encompass streams and lakes represented in the 1:100,000 scale Digital Line Graph (DLG) of surficial hydrography. The HUC boundaries have not been "clipped" to the Wyoming border, in order to maintain the natural boundaries of the units.

This metadata has also been altered from original USGS metadata to be more specific for Wyoming.  

The HUC dataset was compiled originally to provide the National Water Quality Assessment (NAWQA) study units with an intermediate- scale river basin boundary for extracting other GIS data layers. The data can also be used for illustration purposes at intermediate or small scales (1:250,000 to 1:2 million).

This modified dataset was produced under contract with the Wyoming Game and Fish Department for the purpose of wildlife habitat prioritization in Wyoming.  

Calendar_Date: 1994
Currentness_Reference: publication date


Progress: Complete
Maintenance_and_Update_Frequency: none


West_Bounding_Coordinate: -111.98
East_Bounding_Coordinate: -102.13
North_Bounding_Coordinate: 46.37
South_Bounding_Coordinate: 40.38
Theme_Keyword_Thesaurus: None
Theme_Keyword: HUC
Theme_Keyword: GIRAS
Theme_Keyword: hydrologic unit
Theme_Keyword: watershed  
Place_Keyword_Thesaurus: None
Place_Keyword: Wyoming
Access_Constraints: none
These data were digitized at a scale of 1:250,000 and use of these boundaries with larger scale data (i.e. 1:24k hydrography) is not recommended as it would be beyond the resolution capabilities of the data set.

Although the boundaries of the hydrologic units were modified to best match the 1:100,000 scale surficial hydrography DLG, these data should not be considered a 1:100,000 scale product.  

Contact_Person: Mark Negri
Contact_Organization: U.S. Geological Survey, Water Resources Div. (WRD)
Contact_Position: Computer Specialist, Spatial Data Support Unit
Address_Type: mailing address
Address: 12201 Sunrise Valley Drive, MS-445
City: Reston
State_or_Province: VA
Postal_Code: 20191
Country: USA
Contact_Voice_Telephone: 703-648-5613
Contact_Facsimile_Telephone: 703-648-5295
Hours_of_Service: 6:30am-3:30pm EST
Contact_Instructions: May contact thru email or telephone
Data_Set_Credit: USGS Water Resources Division; Tom Kohley, U. of Wyoming
Native_Data_Set_Environment: original data: dgux, 5.4R3.10, AViiON UNIX modified data: Silicon Graphics, ARC/INFO version 7.0.4, in vector polygon format


Label point accuracy was checked by making a point cover of polygon labels from the 1:2,000,000 HUC coverage and then doing an identify of those points in the 1:250,000 scale HUC polygon. This procedure looked for both new or missing polygons, and was also used to check attribute values. Both coverages were also dissolved by accounting unit and comparisons made of the number and location of remaining polygons and corrections made.
Attribute_Accuracy_Value: See Explanation
Attribute accuracy is described, where present, with each attribute defined in the Entity and Attribute Section.
Logical_Consistency_Report: Polygon and chain-node topology present.
Completeness_Report: complete to USGS level four hydrologic unit code
The line work for the HUC coverage was checked against the line work from:

(1) the 1:2,000,000 HUC coverage by plotting both data sets out on one large graphic (about 1:3,000,000). No major discrepancies were found except in coastal areas where the 1:2,000,000 scale coverage had more detail than the 1:250,000 scale coverage.

(2) line work from 1:24,000 scale digitized drainage basins in Colorado, Illinois, and New Jersey. The match was generally good with departures generally less than 2500 meters. The biggest departures were in Colorado and were as large as 4000 meters.

(3) line work from the 1:2,000,000 scale rivers coverage for the USA by plotting both data sets out on one large graphic (about 1:3,000,000). In general the nesting of streams in HUCs was good and HUC boundaries intersected steams at stream intersections.

(4) line work from 1:100,000 scale streams from Colorado, Illinois, and Kansas. The nesting of streams in HUCs was very good. Stream arcs for the most part did not cross HUC arcs except at stream intersections. The error (distance from intersection to HUC line) between HUC lines and stream intersection was less than 500 meters at all intersections checked (about 25).  

Originator: US Geological Survey
Publication_Date: unknown
Title: GIRAS
Source_Scale_Denominator: 250000
Type_of_Source_Media: digital
Calendar_Date: unknown
Source_Currentness_Reference: publication
Source_Citation_Abbreviation: GIRAS
Source_Contribution: main source
Procedures described in this section pertain to conterminous US data: The data was recieived as compressed giras tar files representing either a 1:250,000-scale (1:250K) quadrangle or a 1:100,000-scale (1:100K) quadrangle. Each file was named after its respective quadrangle. A coverage of 1:250k quadrangles was used to divide the country up into four sections and get a list of names for each section. Using GIRASARC2, an aml designed to create an ARC/INFO data-set (coverage) from a GIRAS file and a corresponding neat line coverage.

After the files for a given section were all converted into ARC/INFO format, the outer edge (original neatline) was selected and deleted and the mathematically-calculated neatline coverage from the GIRASNEAT AML program was copied in. The original neatline was replaced with a calculated neatline because in all cases, the outline of the coverage quad never quite conformed to a "true" neatline causing overlaps and gaps between adjacent maps. The new neatline was connected to the internal arcs where they intersected. Lines which did not quite join the new neatline were extended to the edge with a maximum tolerance of 500 meters. All extensions were made within this tolerance. All arcs which extended beyond the new neatline were clipped off. All coverages were checked for additional dangles and then a MAPJOIN was run using NET as the feature option. Finally, most map edgelines were removed from the MAPJOINed coverage to create a seamless basin coverage with polygons (basins) and arcs (boundaries) with attributes.

Errors found in the HUC250 coverage published as OFR 94-0326. Citation U.S. Geological Survey, 1990. Land Use and Land Cover Digital Data from 1:250,000- and 1:100,000-Scale Maps. Data Users Guide 4, 33 pp, Reston Virginia.

Process_Date: 1995
Modifications made by the Wyoming Water Resources Center (WWRC): The WWRC modified the original Hydrologic Unit database by first removing all units that did not drain within the state of Wyoming. For the # remaining units in the state, the boundaries of each unit were modified to better represent the actual drainage area. The hydrologic units for Wyoming were compiled at a scale of 1:250,000 and are often overlaid with the 1:100,000 scale surficial hydrography DLG to produce maps of basin wide hydrography. The overlay of these two layers within the GIS often identified areas where a stream or lake intersected the boundary of the hydrologic unit due (most likely) to the difference in map scale between the two GIS layers

To remove the intersections between hydrologic unit boundaries and streams/lakes in the hydrography DLG, we first assumed that the 1:100,000 scale DLG information was more spatially accurate than the 1:250,000 scale hydrologic unit boundaries. Using this assumption, we modified only the hydrologic unit boundaries in ArcEdit using the hydrography DLG as a background coverage for reference. Elevation (e.g. DEM) was not used as a reference coverage. Changes made to the unit boundaries consisted mostly of boundary extensions in order encompass streams that were in the upper portions of each basin. No new boundaries were added and none were removed.

Process_Date: 1996


Direct_Spatial_Reference_Method: Vector
SDTS_Point_and_Vector_Object_Type: GT-polygon composed of chains
Point_and_Vector_Object_Count: 84


Latitude_Resolution: .001
Longitude_Resolution: .001
Geographic_Coordinate_Units: Decimal Degrees
Horizontal_Datum_Name: North American Datum of 1983
Ellipsoid_Name: GRS1980
Semi-major_Axis: 6378137
Denominator_of_Flattening_Ratio: 298.2572221


For definition of drainage basins, there are two principal tabular data elements of interest. The first, "HUC", stands for the Hydrologic Unit Code and includes the 8-digit cataloging unit as assigned to the basin polygon by the U.S. Geological Survey. The original dataset also contained an attribute, "SOURCE", an attribute of each bounding line segment (arc), incorporating a code to define the source and scale of the source linework. However, in the modifications made specifically to Wyoming, these arc attributes were lost. Reference should be made to the original HUC data available from USGS for this information.

Names for regional units, subregion units, accounting units and cataloging units were added for each of the polygons encompassing Wyoming, as well as the acreage associated with each unit. These attributes are called REG_NAME, SUB_NAME, ACC_NAME, CAT_NAME and ACRES, respectively.  

Entity_and_Attribute_Detail_Citation: Not Available  
Contact_Person: Data Manager
Contact_Organization: Spatial Data and Visualization Center
Address_Type: mailing address
Address: Box 4008 University Station
City: Laramie
State_or_Province: Wyoming
Country: USA
Postal_Code: 82071
Contact_Voice_Telephone: 307-766-2735
Contact_Electronic_Mail_Address: n/a
The distributor shall not be held liable for improper or incorrect use of this data, based on the description of appropriate/inappropriate used described in this metadata document.
Format_Name: ARCE (Arc/Info export)
Format_Version_Number: 7.0.4
Format_Version_Date: 1995
File_Decompression_Technique: Export file was created using defaults, no compression
Network_Resource_Name: or <>
Access_Instructions: <>
Both the ftp and WWW server which this data is available from is a Silicon Graphics Challenge server, running the IRIX 6.2 UNIX operating system.

No fees are required for downloading the data that is on-line. Some fees may be required to cover costs of tapes if data is required on tape media.


Metadata_Date: 199806
Contact_Person: Margo Berendsen
Address_Type: mailing address
Address: Box 4008 University Station
City: Laramie
State_or_Province: Wyoming
Postal_Code: 82071
Country: USA
Contact_Voice_Telephone: 307-766-2735
Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata
Metadata_Standard_Version: FGDC-STD-001-1998

Generated by mp version 2.4.13 on Mon Sep 18 14:39:47 2000