| Geodetic Survey Control Points of Loudoun County, VA (2009) | |
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Data format: SDE Feature Class File or table name: GISDBB.GISBROW.GEODETIC_POINT Coordinate system: Lambert Conformal Conic Theme keywords: location, elevation, geodetic, survey, control, NGS, horizontal, vertical, monument |
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Abstract:
The geodetic control points are the survey reference points registered with the National Geodetic Survey. |
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Metadata elements shown with blue text are defined in the Federal Geographic Data Committee's (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM). Elements shown with green text are defined in the ESRI Profile of the CSDGM. Elements shown with a green asterisk (*) will be automatically updated by ArcCatalog. ArcCatalog adds hints indicating which FGDC elements are mandatory; these are shown with gray text.
The geodetic control points are the survey reference points registered with the National Geodetic Survey.
This layer displays and provides the designation, point identifier, and survey orders of survey control points registered with the National Geodetic Survey.
Data are stored in the corporate ArcSDE Geodatabase as a point feature class. The coordinate system is Virginia State Plane (North), Zone 4501, datum NAD83 HARN. Vertical Datum is assumed to be NAVD88 and has not undergone a vertical transformation or reprojection.
publication date
These data were generated for use by Loudoun County and are available to the public. These data are intended for use at 1:2400 scale or smaller. Acknowledgement of Loudoun County would be appreciated in products derived from this data.
Every reasonable effort has been made to assure the accuracy of these data. Loudoun County, Virginia does not assume any liability arising from the use of these data. These data are provided without warranty of any kind, expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular service. Reliance on these data is at the risk of the user.
1 Harrison St. SE, 2nd Floor
MS 65
Retention of attribute accuracy throughout the coverage to geodatabase feature class conversion process was ensured by a QA/QC programmatic check. To meet satisfactory QA/QC requirements the input coverage and output feature class must have, on a record by record basis, identical attribution when comparing all concatenated fields to all the user-defined attribution.
Topologically Clean
No Ground Truth verification was performed by the County. Features may have been eliminated or generalized due to scale and intended use. To assist Loudoun County, Virginia in the maintenance of the data, please provide any information concerning discovered errors, omissions, or other discrepancies found in the data.
No Ground Truth verification was performed by the County after extraction of original NGS data. Retention of coordinate accuracy throughout the coverage to geodatabase feature class conversion process was ensured by a QA/QC programmatic check. To meet satisfactory QA/QC requirements the input coverage and output feature class must have the same record total, and on a record by record basis, area, perimeter and length differential of less than +/- 0.5%.
Extracted and reprojected control points
The geodetic control point data was extracted from the National Geodetic Survey CD-ROM, reformatted as a comma delimited text file, imported into ArcView as an event theme, exported as a shape file, converted into an Arc/Info coverage, and reprojected from decimal degrees to NAD 1927 Virginia State Plane, North Zone. Refer to "Professional Surveyor", Volume 19, Number 8 dated October 1999 for the detailed procedure for extracting NGS data from the CD-ROM, reformatting it, and creating an ArcView event theme from it.
This data set was part of a batch process that converted legacy data from ArcInfo coverage in Librarian to a single-tiled ArcInfo coverage in preparation for a final conversion to ArcSDE Geodatabase Feature Classes. Data were extracted from Librarian using the EXTRACT TOPOLOGICAL command.
Multi-tiled data sets were extracted into multiple coverages and then combined based on the feature type(s). Layers with both polygon and arc feature classes were processed with the Arc commands MAPJOIN and DISSOLVE. Arc feature classes alone were processed with the Arc commands, APPEND and DISSOLVE. Layers with both arc and point feature classes and point feature classes alone were processed with the Arc command, APPEND. When used, the arc command, DISSOLVE, was given with the <#all> option.
All coverages were then reprojected to HARN83 using the following .prj file specifications:
INPUT
PROJECTION STATEPLANE
UNITS FEET
ZONE 5551
DATUM NAD27 NADCON
PARAMETERS
OUTPUT
PROJECTION STATEPLANE
UNITS FEET
FIPSZONE 4501
DATUM HPGN NADCON
PARAMETERS END
Vertical Datum is NAVD88 and has not undergone a vertical transformation or reprojection. The dataset was then converted to a feature class in a geodatabase in ArcSDE.
The name of the control point assigned by the National Geodetic Survey.
NGS
- An alphanumeric identification given by the NGS; The first two digits are alphabetic, the remaining four digits numeric.
NGS
Horizontal Order of the monument
NGS
First leveling order of position
National Geodetic Service
Second leveling order of position
National Geodetic Service
Third leveling order of position
National Geodetic Service
A leveling order of position
National Geodetic Service
B leveling order of position
National Geodetic Service
Vertical Order of the monument
NGS
First leveling order of position
National Geodetic Service
Second leveling order of position
National Geodetic Service
Third leveling order of position
National Geodetic Service
National Geodetic Service
The source of the data for this point; currently, all points list the NGS as the source.
NGS
Point elevation in meters
Point elevation in meters
Loudoun County
Source that created or modified feature class
Loudoun County
Feature creation or modification date
Loudoun County
Not for public distribution. Internal User ID of editor creating or modifying a feature.
Loudoun County
Feature geometry.
ESRI
Internal feature number.
ESRI
GE_UPD_SOURCE: Source that created or modified feature class
Source Definition 1 Legacy 2 County 3 Contract
1 Harrison Street, S.E., 2nd Floor
MS 65
Every reasonable effort has been made to assure the accuracy of these data. Loudoun County, Virginia does not assume any liability arising from the use of these data. These data are provided without warranty of any kind, expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular service. Reliance on these data is at the risk of the user.
ESRI Geodatabase Feature Class
ESRI Shapefile
AutoCad Digital Exchange File
Size limit: 4.5 GB. Visit our website at: http://www.loudoun.gov/omagi, click on "Loudoun County Mapping Documents & Order Forms." The "Forms" directory will lead you to custom & standard (countywide) data order forms. Hardcopy maps may also be available; please contact the Mapping Office Public Information Counter for more information regarding all data requests.
1 Harrison Street S.E., 2nd Floor
MS 65