Georgia Hydrologic Unit Boundries, 12-digit

Citation:

Citation Information:

Originator: McFadden, Keith W.
Publication Date: unknown
Title: Georgia Hydrologic Unit Boundries, 12-digit.
Geospatial Data Presentation Form: at: Hydrologic Units
Series Information:

Series Name: Digital Data
Issue Identification: 1

Publication Information:

Publication Place: Reston, VA
Publisher: U.S. Geological Survey

Description:

Abstract:
This data set is a digital map of the 8-, 10-, and 12-digit hydrologic unit boundaries for parts of Georgia and parts of Alabama, South Carolina, North
Carolina, and Tennessee. The boundaries were delineated on 1:24,000 7.5
minute USGS topographic quadrangles which were scanned into a digital
image and vectorized interactively on a computer graphic display. The
hydrologic unit polygons are tagged with the appropriate 8, 10, and 12
digit codes.

Purpose:
A watershed approach to investigations and management of water resources requires mapping of appropriate level hydrologic unit
boundaries. The purpose of the hydrologic unit coverage is to provide
and accurate, standardized GIS coverage of watershed boundaries
through the fifth and sixth (10 and 12 digit) hydrologic unit scale
using nationally accepted, consistent methods.

Supplemental Information:
Procedures Used NOTE - Beginning in Feb. 1999 with the Coosa/Tallapossa basins, all
scanning, digitizing, and attribute assignments were transfered to
the USGS Center for Spatial Analysis Technologies (CSAT). Methods and
procedures remained essentially the same.

METHODS FOR SELECTION AND DELINEATION OF HYDROLOGIC UNIT BOUNDARIES
Methods for the selection, delineation, and mapping of Hydrologic Unit
areas are described by Seaber and others (1987), Landers (1997), the
NRCS (1995, draft), and an unfinished guideline being produced by the
Federal Geographic Data Committee (FGDC). The most interpretive
aspect of hydrologic unit mapping is the selection of watersheds and
their downstream outlets for definition as official hydrologic units.
Criteria for these selections in Georgia are described in Landers
(1997). These criteria agree with the FGDC guidelines, and with the
NRCS Guidelines (where applicable). Selected hydrologic units were
reviewed for consensus by the Georgia Interagency Hydrologic Unit
Group in 1996. The selected fourth, fifth, and sixth (8-, 10-, and
12-digit, respectively) hydrologic units were delineated on clean,
unfolded, paper 1:24,000 scale USGS topographic quadrangle maps by
experienced personnel. Each line was checked and color coded on each
map by an experienced hydrologist. The initials of the delineator and
checker are on each quad map, and on a quality assurance review sheet.
The line work of the digital GIS coverage created from the quad maps
was reviewed by two lead hydrologists (Mark Landers and Roger
McFarlane) of the Georgia District office, and hydrologic unit codes
were assigned to each basin. Revisions to line work from this review,
and the correct attribution of HU codes for each polygon were also
checked. The original paper quad maps are currently stored in the
USGS, Georgia District office.

METHOD OF SCANNING PAPER QUADRANGLE MAPS
Paper 1:24,000 7.5 minute USGS topographic quadrangle maps were received
from the Georgia and Alabama District offices. The maps were unrolled,
portions unfolded, and placed on a flat surface for several days to
acclimate. Each map was scanned into a digital TIF image on a PC based
scanning system utilizing a Contex FSS 3012t Full Scale Scanner. The maps
were scanned in 256 shade grayscale at 150 dpi. Each TIF image was given
a name created from the state abbreviation and delineation project quad
number. The TIF images were transferred via FTP to a Silicon Graphics
Indy workstation running Arc/Info 7.1.1.

METHOD OF GEO-REFERENCING SCANNED QUADRANGLE MAPS
Each image was geo-referenced to a decimal degree coordinate system
using the REGISTER command of Arc/Info 7.1.1. The latitiude and
longitude of the four corners of the quadrangles were used as the
reference points. The transformation RMS error for each quadrangle
was recorded and tabulated in the .RMS database file, which is
included as a dataset table. After all quadrangles were registered,
the RMS errors were summed and averaged, and any quadrangles with a
higher than average RMS error were reregistered. The registered TIF
images were transformed and the collar information clipped by the
RECTIFY command using the quadrangle boundary as a clipping box. This
allowed the images to be seamlessly displayed on the computer screen
for easier digitizing and minimizing the error in lines crossing
quadrangle boundaries.

METHOD OF VECTORIZING DELINEATED BOUNDARIES FROM SCANNED MAPS
The geo-referenced images were divided into 11 groups based on the name
of the image. A group of images was assigned to a qualified GIS operator
for vectorization. Each image was loaded into the ArcView 3.0a software
on a PC-based, Data General, or Silicon Graphics system for vectorization.
The image was displayed on the screen at a scale of 1:12,000 as a background
for interactive digitizing of the delineated boundaries. Lines were
digitized with enough vertices to represent the delineated boundaries with
a minimal visual deviation while staying within the required time frame
for completion. The digital linework for each quad was saved as an ArcView
shapefile in a central storage location.

METHOD OF FINAL COVERAGE CREATION
The individual ArcView shapefiles were imported into ArcInfo 7.1.1
coverages through the SHAPEARC command. All coverages were appended
together to create a single Arc/Info coverage. The scanned images
were displayed in ArcEdit as the background with the coverage as the
edit coverage. The display was set to the extent of each of the
scanned quadrangles and the coverage linework was checked for
completion and accuracy. Lines found to be unacceptable or incomplete
through a visual inspection, were redigitized. Special attention was
given to those lines which crossed quadrangle boundaries and
corrections made to those lines if needed. Dangling lines were
corrected to form closed polygons. The coverage was then UNSPLIT to
remove excessive pseudo-nodes and built as a polygon coverage.
Polygons were checked for closure and corrected as needed. Lines were
assigned a number, HUCLINE, to tag them as being 8, 10, or 12 digit
hydrologic boundaries. Polygons were assigned a 12-digit number, HUC,
according to the 1:250,000 paper plots of ennumerated hydrologic units
as supplied by the Georgia District office. Three region feature
layers, HUC8, HUC10, and HUC12, were created by using the
REGIONDISSOLVE command on the polygon layer with HUC as the grouping
item. The region layers, HUC8, HUC10, and HUC12, represent the areas
defined as 8-digit, 10-digit, and 12-digit hydrologic units.
Attributes were added to the polygon and region layers to aid in
selecting, identifying, and displaying hydrologic units based on
various permutations of the hydrologic unit code.

Revisions
Several interim versions were passed between the Georgia and Tennessee
District offices. Those versions were not distributed outside of the
two offices.
pre 01/14/98 - Several versions of the linework only were sent to the
Georgia office for review and correction summaries
01/14/98 - Imported the Florida linework into the coverage
01/15/98 - First version with closed polygons
01/22/98 - First version with tagged polygons and regions
01/23/98 - First version with tagged attributes sent to Georgia
for inital review and correction summary
02/18/98 - Minor corrections were made to the linework and polygons
Coverage was sent to Georgia for review
03/02/98 - Several unneeded outlying arcs were deleted from and
documentation was rewritten.
03/03/98 - Documentation updated. Coverage exported and sent
to Georgia for colleague review
03/30/98 - Completed Ga. District colleague review. Updated documentation.
05/19/98 - Added name attribute columns. Revised title and coverage name.
09/30/98 - Combined Chattahoochee/Flint, and Oconee basins. Added .LUT
table for Basin names, and removed name fields from attribute
tables.
07/20/99 - Data for Coosa/Tallapoosa basins digitized at CSAT and merged
with existing basins. Regions re-built and additional names
added to LUT.
09/01/99 - Savannah and Ogechee basins digitized at CSAT merged into exist
basins. Regions re-built and attributes added.

Reviews Applied to Data
The selection of watersheds for definition as hydrologic units was
reviewed by State of Georgia, Environmental Protection Division and
the Georgia Interagency Hydrologic Unit Group. Each quad map
delineation was checked by USGS personnel. The digital line work was
checked by personnel of the USGS Tennesse District and Georgia
District. Final colleague review was conducted by Keith McFadden and
Jack Alhadeff (USGS), and Tom Mettille (Ga. GIS Data Clearinghouse).

References Cited
Landers, Mark N., 1997, Hydrologic unit mapping in Georgia: Proceedings of
the 1997 Georgia Water Resources Conference, pp. 70-72
Natural Resources Conservation Service, 1995, DRAFT National Instruction
170-304: Mapping and digitizing watershed and subwatershed hydrologic unit
boundaries
Seaber, P.R., Kapinos, F.P., and Knapp, G.L., 1987, Hydrologic Unit Maps:
U.S. Geological Survey Water Supply Paper 2294, 63 pgs.
U.S. Geological Survey, 1975, Hydrologic unit map--1974. State of Georgia:
U.S. Geological Survey, scale 1:500,000. 1 sheet.

Time Period of Content:

Currentness Reference: March 31, 1998

Status:

Progress: Approved
Maintenance and Update Frequency: none planned

Spatial Domain:

Bounding Coordinates:

West Bounding Coordinate: -85.6684184
East Bounding Coordinate: -80.73136817
North Bounding Coordinate: 35.15409737
South Bounding Coordinate: 30.68360081

Keywords:

Theme:

Theme Keyword Thesaurus: None
Theme Keyword: Georgia
Theme Keyword: Alabama
Theme Keyword: hydrologic unit code
Theme Keyword: huc
Theme Keyword: watershed
Theme Keyword: basins

Place:

Place Keyword Thesaurus: None
Place Keyword: Georgia
Place Keyword: Alabama
Place Keyword: South Carolina
Place Keyword: North Carolina
Place Keyword: Tennesee

Access Constraints: none
Use Constraints:
The data set depicts watershed boundaries at a detail suitable for scales of 1:24,000 or smaller.

Security Information:

Security Classification System: None
Security Classification: UNCLASSIFIED
Security Handling Description: None

Native Data Set Environment: Windows_NT Windows_NT, ARC/INFO version 7.2.1

Attribute Accuracy:

Attribute Accuracy Report: See Entity_Attribute_Information
Quantitative Attribute Accuracy Assessment:

Attribute Accuracy Value: See Explanation
Attribute Accuracy 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.
Positional Accuracy:

Horizontal Positional Accuracy:

Horizontal Positional Accuracy Report: none
Quantitative Horizontal Positional Accuracy Assessment:

Horizontal Positional Accuracy Explanation: Resolution as reported

Cloud Cover: 0

Direct Spatial Reference Method: Vector
Point and Vector Object Information:

SDTS Terms Description:

SDTS Point and Vector Object Type: Point
Point and Vector Object Count: 1438

SDTS Terms Description:

SDTS Point and Vector Object Type: String
Point and Vector Object Count: 4734

SDTS Terms Description:

SDTS Point and Vector Object Type: GT-polygon composed of chains'
Point and Vector Object Count: 1481

Horizontal Coordinate System Definition:

Geodetic Model:

Horizontal Datum Name: North American Datum of 1983
Ellipsoid Name: GRS 1980

Unit: Decimal Degrees

Detailed Description:

Entity Type:

Entity Type Label: BASINS24K.PAT
Entity Type Definition: Polygon attribute table
Entity Type Definition Source: ARC/INFO

Attribute:

Attribute Label: -
Attribute Definition: Polygon attribute table
Attribute Definition Source: ARC/INFO
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: -
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: AREA
Attribute Definition: Area of poly/region in square coverage units
Attribute Definition Source: Computed
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: Positive real numbers
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: BASINS24K#
Attribute Definition: Internal feature number
Attribute Definition Source: Computed
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: Sequential unique positive integer
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: BASINS24K-ID
Attribute Definition: User-assigned feature number
Attribute Definition Source: User-defined
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: Integer
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: HUC
Attribute Definition: 12-digit Hydrologic Unit Code
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: none
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: HUC10
Attribute Definition: 10-digit Hydrologic Unit Code
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: none
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: HUC12
Attribute Definition: 12-Digit Hydrologic Unit Code
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: none
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: HUC8
Attribute Definition: 8-digit Hydrologic Unit Code
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: none
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: LAST2
Attribute Definition: Last 2 digits of HUC
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: none
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: LAST4
Attribute Definition: Last 4 digits of HUC
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: none
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: LAST6
Attribute Definition: Last 6 digits of HUC
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: none
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none

Attribute:

Attribute Label: PERIMETER
Attribute Definition: Perimeter of poly/region in coverage units
Attribute Definition Source: Computed
Attribute Domain Values:

Enumerated Domain:

Enumerated Domain Value: Positive real numbers
Enumerated Domain Value Definition: none
Enumerated Domain Value Definition Source: none