1:2,000,000-Scale Hydrologic Unit Boundaries

Frequently-anticipated questions:

• What does this data set describe?
  1. How should this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  3. What similar or related data should the user be aware of?
• How reliable are the data; what problems remain in the data set?
  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How should this data set be cited?

   John Watermolen, U.S. Geological Survey, 200506, 1:2,000,000-Scale Hydrologic Unit Boundaries: National Atlas of the United States, Reston, VA.

   Online Links:

   • <http://nationalatlas.gov/atlasftp.html?openChapters=chpwater#chpwater>

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: 170.87

   East_Bounding_Coordinate: -66.88

   North_Bounding_Coordinate: 71.77

   South_Bounding_Coordinate: 17.68

3. What does it look like?

4. Does the data set describe conditions during a particular time period?

   Calendar_Date: May-2005

   Currentness_Reference: Ground condition

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: Map

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?

      This is a Vector data set. It contains the following vector data types (SDTS terminology):

      • Area point (5348)
      • Complete chain (11576)
      • GT-polygon composed of chains (5348)

   2. What coordinate system is used to represent geographic features?

      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0000716142749. Longitudes are given to the nearest 0.0000716142749. Latitude and longitude values are specified in Decimal degrees.

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is GRS1980.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257222.
      

7. How does the data set describe geographic features?

   Hydrologic Unit (described by HUCS00P020.PAT or Hucs00p020.dbf)

   A subdivision of the Earth, used for the collection and organization of hydrologic data. Regions, subregions, accounting units, and cataloging units are all types of hydrologic units. (Source: National Atlas of the United States)

   Shape

   The representation of the entity in the data. (Source: National Atlas of the United States)

   Value	Definition
   Polygon	2-dimensional element

   Area

   The size of the shape in coverage units. In the distributed file, coverage units represent square decimal degrees. (Source: National Atlas of the United States)

   Range of values
   Minimum:	0.000
   Maximum:	9.069

   Perimeter

   The perimeter of the shape in coverage units. In the distributed file, coverage units represent decimal degrees. (Source: National Atlas of the United States)

   Range of values
   Minimum:	0.004
   Maximum:	41.175

   HUCS00M020# or Hucs00m020

   Internal feature number. (Source: National Atlas of the United States)

   Range of values
   Minimum:	2
   Maximum:	5348

   HUCS00M020-ID (Included in Export format file only.)

   User-assigned feature number. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1
   Maximum:	5345

   Plytype

   A code indicating the classification of offshore polygons. (Source: National Atlas of the United States)

   Value	Definition
   0	Land, including islands.
   2	Open water.

   Huc

   The Hydrologic Unit Code. The code is 8 digits and can be subdivided as follows:

   Digits   Type
   1-2      Water Resource Region
   1-4      Subregion
   1-6      Accounting Unit
   1-8      Cataloging Unit
   
   

   This is the same as Cat. There are six polygons in the file with a Huc of 0; these polygons are not assigned to any hydrologic unit. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1010001
   Maximum:	21020002

   Reg_name

   The Water Resource Region name. (Source: National Atlas of the United States)

   Formal codeset
   Codeset Name:	Hydrologic Unit Maps: Seaber, P.R., Kapinos, F.P., and Knapp, G.L.: U.S. Geological Survey Water-supply Paper 2294; 1987
   Codeset Source:	U.S. Geological Survey

   Formal codeset
   Codeset Name:	Alaska State Hydrologic Unit Map, U.S. Geological Survey map; 1987
   Codeset Source:	U.S. Geological Survey

   Map_label

   A 6-digit character string of the hydrologic unit code. This was created to help map production and a zero was added in front of the single digit regions. (Source: National Atlas of the United States)

   Range of values
   Minimum:	010100
   Maximum:	210200

   Sub_name

   The Subregion name. (Source: National Atlas of the United States)

   Formal codeset
   Codeset Name:	Hydrologic Unit Maps: Seaber, P.R., Kapinos, F.P., and Knapp, G.L.: U.S. Geological Survey Water-supply Paper 2294; 1987
   Codeset Source:	U.S. Geological Survey

   Formal codeset
   Codeset Name:	Alaska State Hydrologic Unit Map, U.S. Geological Survey map; 1987
   Codeset Source:	U.S. Geological Survey

   Acc_name

   The Accounting Unit name. (Source: National Atlas of the United States)

   Formal codeset
   Codeset Name:	Hydrologic Unit Maps: Seaber, P.R., Kapinos, F.P., and Knapp, G.L.: U.S. Geological Survey Water-supply Paper 2294; 1987
   Codeset Source:	U.S. Geological Survey

   Formal codeset
   Codeset Name:	Alaska State Hydrologic Unit Map, U.S. Geological Survey map; 1987
   Codeset Source:	U.S. Geological Survey

   Cat_name

   The Cataloging Unit name. Except in Alaska, this includes the State(s) in which the unit is located. The State name is spelled out except where the cataloging unit name is very long and the cataloging unit is located in several States, in which case the State names are abbreviated with the 2-letter State FIPS code. Occasionally, State names are truncated rather than abbreviated. (Source: National Atlas of the United States)

   Formal codeset
   Codeset Name:	Hydrologic Unit Maps: Seaber, P.R., Kapinos, F.P., and Knapp, G.L.: U.S. Geological Survey Water-supply Paper 2294; 1987
   Codeset Source:	U.S. Geological Survey

   Formal codeset
   Codeset Name:	Alaska State Hydrologic Unit Map, U.S. Geological Survey map; 1987
   Codeset Source:	U.S. Geological Survey

   Huc2

   The number of the Water Resource Region. This is also the first two digits of the Hydrologic Unit Code and is the same as Reg. A region is one of 21 major geographic areas within the U.S. or Caribbean area which contains either the drainage area of a major river or the combined drainage area of a series of rivers. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1
   Maximum:	21

   Huc4

   The number of the Subregion. This is also the first four digits of the Hydrologic Unit Code and is the same as Sub. A subregion is a subdivision of a region and includes the area drained by a river system, a reach of a river and its tributaries in that reach, a closed basin, or a group of streams forming a coastal drainage area. There are 222 subregions. (Source: National Atlas of the United States)

   Range of values
   Minimum:	101
   Maximum:	2102

   Huc6

   The number of the Accounting Unit. This is also the first six digits of the Hydrologic Unit Code and is the same as Act. The accounting units nest within or are equivalent to the subregions. There are 352 accounting units. If the last two digits of this number are 00, the accounting unit and subregion are the same. (Source: National Atlas of the United States)

   Range of values
   Minimum:	10100
   Maximum:	210200

   Reg

   The number of the Water Resource Region. This is also the first two digits of the Hydrologic Unit Code, and is the same as Huc2. A region is one of 21 major geographic areas within the U.S. or Caribbean area which contains either the drainage area of a major river or the combined drainage area of a series of rivers. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1
   Maximum:	21

   Sub

   The number of the Subregion. This is also the first four digits of the Hydrologic Unit Code and is the same as Huc4. A subregion is a subdivision of a region and includes the area drained by a river system, a reach of a river and its tributaries in that reach, a closed basin, or a group of streams forming a coastal drainage area. There are 222 subregions. (Source: National Atlas of the United States)

   Range of values
   Minimum:	101
   Maximum:	2102

   Acc

   The number of the Accounting Unit. This is also the first six digits of the Hydrologic Unit Code and is the same as Huc6. The accounting units nest within or are equivalent to the subregions. There are 352 accounting units. If the last two digits of this number are 00, the accounting unit and subregion are the same. (Source: National Atlas of the United States)

   Range of values
   Minimum:	10100
   Maximum:	210200

   Cat

   The number of the Cataloging Unit. This is the same as Huc. A cataloging unit is currently the smallest element in the hierarchy of hydrologic units, and represents part or all of a surface drainage basin, a combination of drainage basins, or a distinct hydrologic feature. There are 2,264 cataloging units. If the last two digits of this number are 00, the cataloging unit and accounting unit are the same. Cataloging units may also be referred to as watersheds. There are 6 polygons in the file with a Cat of 0; these polygons are not assigned to any hydrologic unit. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1010001
   Maximum:	21020002

   Cat_num

   The number of the Cataloging Unit. This is a redefined Huc or Cat number changed into a character string. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1010001
   Maximum:	21020002

   Hydrologic Unit Boundary (described by HUCS00L020.AAT or Hucs00l020.dbf)

   A boundary between hydrologic units. (Source: National Atlas of the United States)

   Shape

   The representation of the entity in the data. (Source: National Atlas of the United States)

   Value	Definition
   Polyline	1-dimensional element that surrounds a 2-dimensional element.

   Fnode# or Fnode_

   Internal sequence number of the from-node. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1
   Maximum:	9039

   Tnode# or Tnode_

   Internal sequence number of the to-node. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1
   Maximum:	9039

   Lpoly# or Lpoly_

   Internal sequence number of the left polygon. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1
   Maximum:	5348

   Rpoly# or Rpoly_

   Internal sequence number of the right polygon. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1
   Maximum:	5347

   Length

   The length of the line in coverage units. In the distributed file, coverage units represent decimal degrees. (Source: National Atlas of the United States)

   Range of values
   Minimum:	0.000
   Maximum:	6.143

   US_HUCS_ALB# or Hucs00m020

   Internal feature number. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1
   Maximum:	11576

   US_HUCS_ALB-ID (Included in Export format file only.)

   User-assigned feature number. (Source: National Atlas of the United States)

   Range of values
   Minimum:	1
   Maximum:	11576

   Bndtype

   The code number describing the location or type of the hydrologic unit boundary. Boundaries occur between hydrologic units and between onshore and offshore parts of the same hydrologic unit. (Source: National Atlas of the United States)

   Value	Definition
   0	Coastline or International Boundary separating offshore and onshore parts of the same hydrologic unit.
   2	Land and occasionally water boundary between two Water Resource Regions.
   4	Land and occasionally water boundary between two Subregions.
   6	Land and occasionally water boundary between two Accounting Units.
   8	Land and occasionally water boundary between two Cataloging Units.

   Error_type

   A code indicating the type of conflict between the streams file and the hydrologic unit boundary. (Source: National Atlas of the United States)

   Value	Definition
   0	No conflict exists.
   4	There was an error in the streams file. The hydrologic unit Boundary was not changed.
   5	There was a conflict between the NMD streams data and the 1:500,000-scale Hydrologic Unit Boundaries map. The hydrologic unit boundary was changed to agree with the streams.

Who produced the data set?

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • John Watermolen, U.S. Geological Survey

2. Who also contributed to the data set?

   Others who have helped with this map layer and the metadata include Steve Denowski, Greg Allord, Curtis Price, Ken Lanfear and David Lorenz, in addition to other colleagues within the U.S. Geological Survey.

3. To whom should users address questions about the data?
   U.S. Geological Survey
   CAPP Chief
   505 Science Dr.
   Madison, WI 53711-1061
   USA
   

   608-238-9333 (voice)
   608-238-9334 (FAX)
   atlasmail@usgs.gov
   

Why was the data set created?

These data are intended for geographic display and analysis at the national level, and for large regional areas. The data should be displayed and analyzed at scales appropriate for 1:2,000,000-scale data. No responsibility is assumed by the U.S. Geological Survey or the National Atlas of the United States in the use of these data.

How was the data set created?

1. From what previous works were the data drawn?

   HUCmaps (source 1 of 15)

   U.S. Geological Survey, 1974-1987, State Hydrologic Unit Maps (for each State): U.S. Geological Survey, Office of Water Data Coordination, Reston, VA.

   Online Links:

   • <http://water.usgs.gov/GIS/huc.html>

   Type_of_Source_Media: Mylar separate

   Source_Scale_Denominator: 500,000

   Source_Contribution: Linework for the map layer.

   Seaber (source 2 of 15)

   Seaber, Paul R., Kapinos, F. Paul, and Knapp, George L., 1987, Hydrologic Unit Maps: Water-Supply Paper 2294, U.S. Geological Survey, Reston, VA.

   Online Links:

   • <http://water.usgs.gov/GIS/huc.html>

   Type_of_Source_Media: Paper map

   Source_Contribution: Cataloging unit names for all States except Alaska.

   HUCAKmap (source 3 of 15)

   U.S. Geological Survey, 1987, Alaska State Hydrologic Unit Map: U.S. Geological Survey, Reston, VA.

   Online Links:

   • <http://water.usgs.gov/GIS/huc.html>

   Type_of_Source_Media: Mylar separate

   Source_Scale_Denominator: 2,500,000

   Source_Contribution:

   The source contributed line work and names for hydrologic units in Alaska.

   DLGHY (source 4 of 15)

   U.S. Geological Survey, 1972-1980, 1:2,000,000 DLG Hydrography: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Location of streams for accuracy testing.

   HUCS10 (source 5 of 15)

   U.S. Geological Survey, 1986, Hydrologic Unit Codes map: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Intermediate digital file.

   HUCS11 (source 6 of 15)

   U.S. Geological Survey, 1992, Hydrologic Unit Codes map: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Intermediate digital file.

   HUCS111 (source 7 of 15)

   U.S. Geological Survey, 1994, Hydrologic Unit Codes map: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Intermediate digital file.

   DLGCO (source 8 of 15)

   U.S. Geological Survey, 1989, 1:2,000,000 County Boundaries: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution:

   Determination of boundaries for identification of offshore and onshore areas.

   RF1 (source 9 of 15)

   U.S. Environmental Protection Agency, 1975, Reach File Version 1.0 Alpha: U.S. Environmental Protection Agency, Washington, DC.

   Type_of_Source_Media: Digital file

   Source_Contribution: Information on flow between cataloging units.

   NAStates (source 10 of 15)

   U.S. Geological Survey, 1998, State Boundaries of the United States: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Coastline information

   NAHydro (source 11 of 15)

   U.S. Geological Survey, 1998, Hydrography Features of the United States (linear): U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Coastline information

   HUCS20 (source 12 of 15)

   U.S. Geological Survey, 19990401, 1:2,000,000-Scale Hydrologic Unit Boundaries: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Spatial and attribute information.

   HUCS21 (source 13 of 15)

   U.S. Geological Survey, 200104, 1:2,000,000-Scale Hydrologic Unit Boundaries: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Spatial and attribute information.

   HUCS22 (source 14 of 15)

   U.S. Geological Survey, 200201, 1:2,000,000-Scale Hydrologic Unit Boundaries: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Spatial and attribute information.

   HUCS23 (source 15 of 15)

   U.S. Geological Survey, 200211, 1:2,000,000-Scale Hydrologic Unit Boundaries: U.S. Geological Survey, Reston, VA.

   Type_of_Source_Media: Digital file

   Source_Scale_Denominator: 2,000,000

   Source_Contribution: Spatial and attribute information.

2. How were the data generated, processed, and modified?

   Date: 1985 (process 1 of 8)

   The original hydrologic unit boundaries file (HUCS10) was created through the following steps:

   a) 1:2,000,000-scale stable-base map plots of drainage (streams) and
   the latitude/longitude grid were obtained from the USGS National
   Mapping Division (NMD).  These plots were in the Lambert Conformal
   Conic projection, and used 1:500,000-scale State base map projection
   parameters.  Fifteen sections were plotted using 1970 National Atlas
   1:2,000,000-scale sectional boundaries.
   
   b) Individual State 1:500,000-scale hydrologic unit maps in the Lambert
   Conformal Conic projection were photoreduced to 1:2,000,000.
   
   c) Hydrologic unit boundaries were compiled and the edges were matched
   on scale-stable 1:2,000,000 plots.  The boundaries were combined with
   the streams plots for digitizing.
   
   d) The hydrologic unit boundaries were digitized by Automated Datatron,
   Hyattsville, MD, which digitizes materials on contract for NMD.
   
   e) Digital data from Automated Datatron was converted to an ArcInfo
   coverage, then checked and corrected.
   
   f) A detailed, annotated list was compiled, listing locations where
   hydrologic unit boundaries and streams were coincident, or where
   1:2,000,000-scale DLG streams were in error.  Wherever possible,
   conflicts and errors were resolved.
   

   Data sources used in this process:

   • HUCmaps
   • DLGHY

   Data sources produced in this process:

   • HUCS10

   Date: 1992 (process 2 of 8)

   HUCS11 was created by modifying and correcting the HUCS10 file in ArcInfo, and combining it with a 1:2,000,000-scale U.S. counties file to identify onshore and offshore areas. Other county attributes were excluded. This process was done in ArcInfo, and used a fuzzy tolerance of 2 meters. A small part of the original map, which laid on top of part of the Canadian Great Lakes, was deleted. The attributes were renamed and expanded.

   Data sources used in this process:

   • HUCS10
   • DLGCO

   Data sources produced in this process:

   • HUCS11

   Date: 1994 (process 3 of 8)

   A HUCs_2M.TRACE file was created from the River Reach 1 (rf1) coverage, which includes a pointer to the next downstream segment of each reach. The resulting file was added to INFO, along with an index created using the INDEX_HUC.AML. These files are included in HUCS111 only and are not in the distributed version of the Hydrologic Unit Boundaries map layer.

   Data sources used in this process:

   • HUCS11
   • RF1

   Data sources produced in this process:

   • HUCS111

   Date: 1998 (process 4 of 8)

   Using ArcInfo, HUCS111 was compared with the most recent 1:2,000,000- scale streams file created by the USGS National Mapping Division (NMD) for inclusion in the National Atlas of the United States of America. Where a stream crossed a hydrologic unit boundary, the boundary was compared to the 1:500,000-scale State hydrologic unit map (Seaber). If a stream and hydrologic unit boundary intersection could not be resolved by this comparison, the USGS 1:100,000-scale topographic quadrangles were used. All corrected hydrologic unit boundaries were given a value of 5 for the Error_type attribute. The boundaries were changed by moving vertices to include the stream in the appropriate hydrologic unit. All editing was done on-screen. This step happened May 22, 1998 and November 10, 1998.

   The Region, Subregion, Accounting unit, and Cataloging unit names from Seaber were added to the map layer and spot-checked. Cataloging unit names for Alaska were added from the Alaska Hydrologic Unit Map (HUCAKmap).

   Values for BNDTYPE were determined from the bounding polygons using INDEX_HUC.AML. The attributes Error_type, Reg_name, Map_label, Cat_Name, and Cat_num were added to the file.

   Two annotation layers were also added to the coverage. One layer is called anno.maplabel1, which shows the first six digits for each accounting unit. The labels for accounting Regions 1 though 9 have the "0" in front of the number. The second annotation layer is anno.catnum, and this layer has the last 2 digit codes for each cataloging unit. All numbers were checked manually on a 1:2,000,000-scale plot of the data set. The cataloging unit names were spot-checked. The file was modified to agree with the official National Atlas coastline (NAStates)

   The ArcInfo coverage was exported to create the shapefiles and SDTS files.

   Data sources used in this process:

   • HUCS111
   • Seaber
   • HUCAKmap
   • NAStates
   • NAHydro

   Data sources produced in this process:

   • HUCS20

   Date: 2001 (process 5 of 8)

   The HUCS20 file was modified and corrected in ArcInfo. Two Hydrologic unit codes were corrected. The first error was in western Illinois, Region 07, Subregion 08, Accounting unit 01, where cataloging unit 04 was incorrectly tagged 07. The second error was in northeastern Missouri, Region 07, Subregion 11, Accounting unit 00, Cataloging unit 01, where the subregion was incorrectly tagged 10.

   Misspelled names in sub_name, acc_name, and cat_name were corrected. The file was exported to create new shapefiles and SDTS files.

   Data sources used in this process:

   • HUCS20

   Data sources produced in this process:

   • HUCS21

   Date: Jan-2002 (process 6 of 8)

   The HUCS21 file was modified and corrected in ArcGIS. One Hydrologic Unit code was corrected in Oregon. Region 17, Subregion 07, Accounting unit 03, Cataloging unit 01 had all user-defined attribute items incorrectly valued as Region 17, Subregion 09, Accounting unit 00, Cataloging unit 05.

   Data sources used in this process:

   • HUCS21

   Data sources produced in this process:

   • HUCS22

   Date: Nov-2002 (process 7 of 8)

   The HUCS22 file was modified and corrected in ArcGIS. One cataloging unit name was corrected in Oregon. Region 17, Subregion 10, Accounting unit 02, Cataloging unit 03 had the attribute CAT_NAME incorrectly valued as Wilson-Trusk-Nestuccu, Oregon. It was corrected to Wilson-Trask-Nestucca, Oregon.

   Data sources used in this process:

   • HUCS22

   Data sources produced in this process:

   • HUCS23

   Date: May-2005 (process 8 of 8)

   The HUCS23 file was modified and corrected in ArcGIS. Cataloging unit 03050201 had the attribute CAT_NAME incorrectly valued as Copper, South Carolina. It was corrected to Cooper, South Carolina. HUC 1103 Sub_name was incorrectly valued as Middel Arkansas. It was corrected to Middle Arkansas. The codes and all attributes in the following basins were corrected: Cataloging unit 9030006 corrected from 9030004, Cataloging unit 12100204 corrected from 12100303, and Cataloging unit 17060206 corrected from 17060203.

   Data sources used in this process:

   • HUCS23

3. What similar or related data should the user be aware of?

   U.S. Geological Survey, 1974-1987, State Hydrologic Unit Map (for each State): U.S. Geological Survey, Reston, VA.

   Online Links:

   • <http://water.usgs.gov/GIS/huc.html>

How reliable are the data; what problems remain in the data set?

1. How well have the observations been checked?

   The arc attributes were manually checked by assigning unique line weights and colors to the values, and then plotting the data. The plots were then compared to the source.

   The polygon attributes were checked by comparing a 1:2,000,000-scale plot to the source. The attribute accuracy is estimated at 99%.

2. How accurate are the geographic locations?

   The accuracy of the original map layer was checked by comparing the digital files to several data sources. First, both the line work and the polygon labels were checked against the source compilation. No digitization errors were found during this phase.

   Next, the hydrologic unit boundaries were compared to the 1970 1:2,000,000-scale DLG stream file and the 1:500,000-scale Hydrologic Unit Maps. Plots containing both the streams and the hydrologic unit boundaries were made at a scale of 1:2,000,000. Hydrologic unit boundary intersections were checked, as well as problem areas such as points where streams crossed hydrologic unit boundaries on the plot but not on the hydrologic unit map. More than 400 errors were found. All errors that could be corrected were corrected. The remaining errors could not be corrected because the streams were in error rather than the hydrologic unit boundaries.

   Finally, the hydrologic unit boundaries were plotted at 1:2,000,000 scale and compared to the NMD 1998 1:2,000,000-scale hydrologic data set. Any discrepancies were addressed by reference to either the 1:500,000-scale or the 1:100,000-scale maps. The exceptions to this were the hydrologic unit boundaries for Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands. The Alaska boundaries were checked on a 1:2,500,000-scale plot but not modified, because the boundaries cross glaciers, and it is difficult to distinguish flow from the glaciers. The Hawaii hydrologic unit boundaries were not reviewed because each island represents a cataloging unit. The Puerto Rico and U.S. Virgin Islands boundaries were not plotted but were reviewed on-screen using a 1:1,000,000 hydrologic map layer created for the 1991 National Water Summary.

   The horizontal positional accuracy of the data matches the positional accuracy of the original compilation.

3. How accurate are the heights or depths?

4. Where are the gaps in the data? What is missing?

   This file contains hydrologic unit boundaries and codes for all 50 States, Puerto Rico, and the U.S. Virgin Islands. Boundaries and codes are included for regions, subregions, accounting units, and cataloging units.

5. How consistent are the relationships among the observations, including topology?

   Polygon and chain-node topology are present. All polygons are labeled and were tested by using the ArcInfo command labelerrors. All polygons were checked for closure and intersections by using the ArcInfo intersecterr command. The file is clean.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?

Access_Constraints: None

Use_Constraints:

None. Acknowledgment of the National Atlas of the United States of America and (or) the U.S. Geological Survey would be appreciated in products derived from these data.

1. Who distributes the data set? (Distributor 1 of 1)
   Earth Science Information Center, U.S. Geological Survey
   507 National Center
   Reston, VA 20192
   USA
   

   1-888-ASK-USGS (1-888-275-8747) (voice)
   

   Contact_Instructions:

   In addition to the address above there are other ESIC offices throughout the country. A full list of these offices is at <http://ask.usgs.gov/esic_index.html>.

2. What's the catalog number I need to order this data set?

3. What legal disclaimers am I supposed to read?

   Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made by the U.S. Geological Survey regarding the utility of the data on any other system, nor shall the act of distribution constitute any such warranty.

4. How can I download or order the data?
   • Availability in digital form:

     Data format:	ARCE
     Network links:	<http://nationalatlas.gov/atlasftp.html?openChapters=chpwater#chpwater>

     Data format:	ESRI Shapefile
     Network links:	<http://nationalatlas.gov/atlasftp.html?openChapters=chpwater#chpwater>

     Data format:	SDTS
     Network links:	<http://nationalatlas.gov/atlasftp.html?openChapters=chpwater#chpwater>

   • Cost to order the data: There is no charge for the map layer.

Who wrote the metadata?

Dates:

Last modified: 24-Mar-2006

Metadata author:

U.S. Geological Survey
CAPP Chief
505 Science Dr.
Madison, WI 53711-1061
USA

608-238-9333 (voice)
608-238-9334 (FAX)
atlasmail@usgs.gov

Metadata standard:

FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)