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Southern California Hydrography Metadata Image of Southern California Study Area



    National Hydrography Dataset (NHD) of stream reaches at 1:100,000 scale 
    for the Southern California Pilot Study Area.
    This geodataset contains the Southern California Pilot Study Area NHD, a 
    feature-based database that interconnects and uniquely identifies the 
    stream segments or reaches that comprise the nations surface water 
    drainage system. 
Data Type:
    Coverage, line
Data Originators:
    U.S. Geological Survey 
    Reston, VA
    U.S. Environmental Protection Agency
    Office of Water
    Washington, DC
Data Processor:
    Ed Evanson
    Lockheed Martin Environmental Services
    1050 E. Flamingo Road, Suite E120
    Las Vegas, NV 89119
Data Provider:
    Dan Heggem
    U.S. Environmental Protection Agency NERL
    P.O. Box 93478
    Las Vegas, NV 89193-3478
    hydrography, NHD, RF3, stream reaches, Southern California, Pilot Study Area
Revision Number:
Series Name:                    
Online Link (URL):              
Time Period of Content: 
    Published 1999.        
Use Constraints:
    None. Acknowledgment of the originating agencies would be appreciated in
    products derived from these data.
    Southern California data browser
Date of metadata entry/update:
No Publication Information Available
No File Security Information Available
Cloud Cover:
    Not applicable
    Arc/Info 7.2.1 Patch 2
Operating System:
    Unix Sun Solaris 2.6
Path Name:
Logical Consistency Report:
    Not presently available
Completeness Report:
    Not presently available
Horizontal Positional Accuracy:
    Not presently available
Vertical Positional Accuracy:
    Not presently available
Attribute Accuracy:
    Not presently available
    Using an AML script, the required raw NHD (*.gz) files for the study 
    area were uncompressed and unarchived.  The NHD coverages were copied 
    out of the workspaces and were cleaned to a very low tolerance and then 
    appended together.  All required (external) Info feature tables and 
    attribute files were automatically copied to the NHD output coverage 
    during the append operation.  The appended NHD coverage was reprojected 
    to the study area projection, cleaned again to a very low tolerance, 
    then clipped to the study area boundary.
Reviews Applied to Data    
    Lockheed Martin Environmental Services internal review
Related Spatial Data Files:
    All geodatasets with sca_ prefix.
Other References Cited:  
Update Frequency:
    As needed

              Description of DOUBLE precision coverage sca_nhda83
                                FEATURE CLASSES
                                    Number of  Attribute     Spatial
Feature Class          Subclass     Features   data (bytes)  Index?   Topology?
-------------          --------     ---------  ------------  -------  ---------
ARCS                                    16696        32
POLYGONS                                 2349        24               Yes
NODES                                   15556        48
ROUTES/SECTIONS              LM        81/116    152/32
                          DRAIN    2486/14961     54/32
                            RCH    7793/14949    150/32
REGIONS                      LM            82       200               Yes
                             WB           703       204               Yes
                            RCH           569       166               Yes
                               SECONDARY FEATURES
Tics                                        4
Arc Segments                           319746
Polygon Labels                           2348
Fuzzy   =                 0.000 V          Dangle  =                 0.000 V
                               COVERAGE BOUNDARY
Xmin =              -361014.312            Xmax =                41579.233
Ymin =              3395346.849            Ymax =              3655256.075
The coverage has not been Edited since the last BUILD or CLEAN.
                          COORDINATE SYSTEM DESCRIPTION
Projection               ALBERS
Datum                     NAD83
Units                    METERS             Spheroid                GRS1980
1st standard parallel                                   33 15  0.000
2nd standard parallel                                   40 15  0.000
central meridian                                       -116 45  0.00
latitude of projection's origin                          0  0  0.000
false easting (meters)                                       0.00000
false northing (meters)                                      0.00000

Annotation Name:


 TYPE NAME                            INTERNAL NAME    NO. RECS LENGTH EXTERNL
  DF  SCA_NHDA83.TIC                    ARC0366DAT           4      20    XX
  DF  SCA_NHDA83.NAT                    ARC0367DAT       15556      48    XX
  DF  SCA_NHDA83.SECLM                  ARC0368DAT         116      32    XX
  DF  SCA_NHDA83.RATLM                  ARC0369DAT          81     152    XX
  DF  SCA_NHDA83.SECDRAIN               ARC0370DAT       14961      32    XX
  DF  SCA_NHDA83.RATDRAIN               ARC0371DAT        2486      54    XX
  DF  SCA_NHDA83.SECRCH                 ARC0372DAT       14949      32    XX
  DF  SCA_NHDA83.RATRCH                 ARC0375DAT        7793     150    XX
  DF  SCA_NHDA83.PATLM                  ARC0376DAT          82     200    XX
  DF  SCA_NHDA83.PATWB                  ARC0377DAT         703     204    XX
  DF  SCA_NHDA83.PATRCH                 ARC0378DAT         569     166    XX
  DF  SCA_NHDA83.BND                    ARC0379DAT           1      32    XX
  DF  SCA_NHDA83.PAT                    ARC0392DAT        2349      24    XX
  DF  SCA_NHDA83.AAT                    ARC0393DAT       16696      32    XX

FGDC Content Standards for Digital Geospatial Metadata
FGDC Standards Version 6/98 / metadata.aml ver. 1.3 5/21/99


The National Hydrography Dataset (NHD) is a feature-based database that
interconnects and uniquely identifies the stream segments or reaches that
comprise the nations surface water drainage system. It is based initially on
the content of the U.S. Geological Survey 1:100,000-scale Digital Line Graph
(DLG) hydrography data, integrated with reach-related information from the U.S.
Environmental Protection Agency Reach File Version 3.0 (RF3). More
specifically, it contains reach codes for networked features and isolated
lakes, flow direction, names, stream level, and centerline representations for
areal water bodies. Reaches are also defined to represent 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 set out by the Federal Geographic Data

The National Hydrography Dataset combines elements of the DLG and RF3: spatial
accuracy and comprehensiveness from the DLG and network relationships, names,
stream level, and a unique identifier (reach code) for surface water features
from RF3. The NHD supersedes DLG and RF3 by incorporating them, not by
replacing them. Users of DLG and RF3 will find the National Hydrography Dataset
both familiar and greatly expanded and refined. The NHD provides a national
framework for assigning reach addresses to water-related entities, such as
industrial dischargers, 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 in a
manner similar to street addresses. 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 better 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. The
National Hydrography Dataset is designed to provide comprehensive coverage of
hydrologic data for the U.S. While initially based on 1:100,000-scale data, the
NHD is designed to incorporate - and encourage the development of -
higher-resolution data required by many users. It will facilitate the improved
integration of water-related data in support of the application requirements of
a growing national user community and will enable shared maintenance and

Attribute Accuracy Report:
The accuracy of the attributes of the Digital Line Graph data 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 digital line graph 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 on reaches were validated against a
March 1999 extract from the Geographic Names Information System. The entry and
identifier for the names match those in the Geographic Names Information
System. The association of each name to reaches has not been methodically
checked, and so a name may be applied to the wrong reaches. Anecdotal reviews
indicate that 80 percent or more of the named reaches have the correct name.
Reaches were delineated with a batch procedure and were checked extensively
during the visual pass steps of processing. Based on automated quality
assurance/quality control checks performed at various intervals during the
processing, approximately 99 percent of the reaches are delineated according to

Logical Consistency Report:
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

Completeness Report:
The completeness of the data reflects the content of the sources, which, in the
initial release of the National Hydrography Dataset, most often are U.S.
Geological Survey topographic maps. Features found on the ground may have been
eliminated or generalized on the source graphic 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 (approximately 2.4 hectares) were
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. A priority for maintenance of the National
Hydrography Dataset is the rectification of these differences. Transport
reaches are defined on nearly all features of type stream/river, canal/ditch,
artificial path, pipeline, and connector. Waterbody reaches are defined on the
subset of lake/pond features that were identified as waterbodies during the
development of Reach File Version 3. Most attention in applying geographic
names was given to transport reaches that follow stream/rivers and waterbody
reaches. Near the international boundaries with Canada and Mexico, only the
parts of features within the United States are delineated. Detailed capture
conditions are provided for every feature type in the Standards for National
Hydrography Dataset (USGS, 1999), available online through

Horizontal Positional Accuracy Report:
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 their true position. Additional offsets to positions may have
been introduced where there are many features 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 to
assess the positional accuracy of digital data. Linear features of the same
type along the adjoining edges of data sets are aligned if they are within a
0.02 inch tolerance (at map scale). To align the features, the midpoint between
the end of the corresponding features is computed, and the ends of features are
moved to this point. Features outside the tolerance are not moved; instead, a
feature of type connector was added to join the features.

Vertical Positional Accuracy Report:
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.

Entity and Attribute Overview:
The National Hydrography Dataset is a comprehensive set of digital spatial
data that encodes information about naturally occurring and constructed 
bodies of water, paths through which water flows, and related entities. 
The information encoded about features includes classification by type, 
other characteristics, a unique common identifier, the feature length or 
area, and (rarely) the elevation of the surface of water pools and a 
description of the stage of the elevation. For reaches, encoded information
includes a reach code, the date the reach code was assigned, a unique 
common identifier, the reach length or area, and, for transport reaches, 
the stream level. Geographic names, and their identifiers in the Geographic
Names Information System, are assigned to reaches or, if no reach is 
available, to features. The data also contain relations among reaches that
encode the direction of water flow, metadata, and information that supports
the exchange of future updates and improvements to the data.

Entity and Attribute Detail Citation:
The names and definitions of all feature types, characteristics, and values
are in U.S. Geological Survey, 1999, Standards for National Hydrography 
Dataset: Reston, Virginia, U.S. Geological Survey. The document is available
online through http://mapping.usgs.gov/standards/. Information about tables
and fields in the data are available from the user documentation for the 
National Hydrography Dataset.

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