| Geologic Outcrop Structures of Loudoun County, VA (2009) | |
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Data format: SDE Feature Class File or table name: GISDBB.GISBROW.GEOLOGY_STRUCTURE_POINT Coordinate system: Lambert Conformal Conic Theme keywords: geoscientificInformation, Geology, Geologic, Bedrock, Fault, Structure, Surficial, Outcrop, Strike, Dip |
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Abstract:
"Structure" is one of four layers which collectively describe the subsurface geologic formation, structural geology and surficial deposits. "Structure" is the point file of geologic strike and dip as determined from outcrops.
The geology of Loudoun County, Virginia, was mapped in 1988 through 1991 under a cooperative agreement between the U.S. Geological Survey (USGS) and the Loudoun County Department of Environmental Resources. This geologic map was compiled in 1993 from a series of detailed published and unpublished field investigations at scales of 1:12,000 and 1:24,000. Some of these same data were compiled as a digital geologic map at 1:100,000 scale (Burton and others, 1992a) and were the basis for a cost-benefit analysis of the societal value of geologic maps (Bernknopf and others, 1993).
The data was later revised and published by USGS in the Open File Report, MAP OF-99-150, GEOLOGIC MAP OF LOUDOUN COUNTY, VIRGINIA By Scott Southworth, W.C. Burton, J.S. Schindler, and A.J. Froelich1 with contributions on the geology of the Piedmont province by A.A. Drake, Jr., and R.E. Weems and an aeromagnetic survey by D.L. Daniels, W.F. Hanna, and R.E. Bracken. |
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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.
"Structure" is one of four layers which collectively describe the subsurface geologic formation, structural geology and surficial deposits. "Structure" is the point file of geologic strike and dip as determined from outcrops.
The geology of Loudoun County, Virginia, was mapped in 1988 through 1991 under a cooperative agreement between the U.S. Geological Survey (USGS) and the Loudoun County Department of Environmental Resources. This geologic map was compiled in 1993 from a series of detailed published and unpublished field investigations at scales of 1:12,000 and 1:24,000. Some of these same data were compiled as a digital geologic map at 1:100,000 scale (Burton and others, 1992a) and were the basis for a cost-benefit analysis of the societal value of geologic maps (Bernknopf and others, 1993).
The data was later revised and published by USGS in the Open File Report, MAP OF-99-150, GEOLOGIC MAP OF LOUDOUN COUNTY, VIRGINIA By Scott Southworth, W.C. Burton, J.S. Schindler, and A.J. Froelich1 with contributions on the geology of the Piedmont province by A.A. Drake, Jr., and R.E. Weems and an aeromagnetic survey by D.L. Daniels, W.F. Hanna, and R.E. Bracken.
Geology was researched and compiled for use in studies of soils and groundwater, and to support the County's water resources plan.
Data are published by USGS at http://geology.er.usgs.gov/eespteam/GISLab/Search/Virginia/loudoun/index.html Files are available as ESRI shapefile and .e00 files. Data were originally prepared in Lat/Long (NAD27) and have been reprojected by the County to Virginia State Plane (North), Zone 4501, datum NAD83 HARN, US Feet. Data are stored in the corporate ArcSDE geodatabase as a point feature class.
For additional information, please see the geology supplements:
GEOLOGIC MAP OF LOUDOUN COUNTY, VIRGINIA
REPORT TO ACCOMPANY MAP OF-99-150
U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY
Southworth, et. al. (1999)
and
Interpretive Guide to Geology and Groundwater in Loudoun County, VA
Loudoun County, VA, Dept. of Environmental Resources (1993)
March 2004
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. 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.
1 Harrison Street S.E., 2nd floor
MS 60A
Originator, USGS, provided no accuracy assessment
Topologically Clean
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.
Originator, USGS, provided no accuracy assessment
Pete Chirico
USGS provide ESRI shapefiles in latitude and longitude decimal degrees and .e00 files are in UTM 18 NAD83. Using ArcToolBox, the .e00 files were projected to Virginia State Plane North, HARN, US Survey feet using the Virginia HARN correction. This was done in two-step process. First projection is from UTM to NAD 83 and then from NAD83 to HARN.
ESRI coverage format-specific items that no longer apply were deleted upon conversion to SDE Geodatabase. These items include <COVER>#, <COVER>-ID, FNODE#, TNODE#, LPOLY#, RPOLY#, LENGTH, AREA, and PERIMETER.
Unknown
USGS
Confidence of digitize point location
USGS
Geologic dip angle ranging from 0 to 90 (vertical bedding)
USGS
Strike azimuth. Often has a value of zero, but sometimes it is the same value as ST_AZ.
USGS
Appears to have most complete set of values for azimuth, presumably the strike angle. It is unknown if this is a clockwise or counterclockwise rotation angle and whether this is from north (geographic) or east (arithmetic).
USGS
Symbol rotation (arithmetic). Note ST_SYMBOL_ANG & ANGLE differ by 180 or -180 degrees, indicating complimentary angles. The difference is zero if the field ST_ROTATION has value of C or CC.
USGS
Dip direction
USGS
ST_ROTATION: Rotation of geologic strike and dip of outcrop and ground surface.
USGS
Source which created or modified feature class
Loudoun County
Not for public distribution. Interal User ID of editor creating or modifying feature class.
Loudoun County
Internal feature number.
ESRI
Feature geometry.
ESRI
ST_DIGPT: Confidence of digitized point location. Created by USGS, interpratiation on coded values by Loudoun County
Confidence Definition C Confident point digitized E Estimated point location digitized
ST_ROTATION: Rotation of geologic strike and dip of outcrop and ground surface. Usually blank. Two values of V that are vertical, but not all 90 degree dips are V for rotation. This does not appear to be consistent.
Rotation Definition C Clockwise CC Counterclockwise V Vertical
ST_UPD_SOURCE: Source which created or modified feature class
Source Definition 0 Undetermined 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 Personal 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