The Central African Republic Diamond Database (2018) - Watersheds of Large Rivers

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Frequently anticipated questions:

What does this data set describe?

Title:
The Central African Republic Diamond Database (2018) - Watersheds of Large Rivers
Abstract:
This vector GIS dataset contains polygons that delimit the watershed boundaries of 6th order streams in the Central African Republic. It was derived from the 30m Hydrologically Corrected Digital Elevation Model (DEM) of the Central African Republic using the tools in ArcGIS 10.4. In brief, this process entails calculation of flow direction and flow accumulation raster datasets from the DEM; classification of the flow accumulation raster into gridcells representing the location of a stream (based on the blue lines of the 1:250,000 Joint Operations Graphic for CAR); calculation of the Strahler Stream Order; reclassification of the stream raster to remove lower order stream segments (orders 1-5); calculation of a stream link raster, which entailed enumeration of the reclassified stream's intersections; and calculation of watershed areas based on the stream link raster and the flow direction raster. Details regarding these procedures can be found in DeWitt and others (2018).
  1. How might this data set be cited?
    DeWitt, Jessica D., Chirico, Peter G., Bergstresser, Sarah E., and Clark, Inga E., 2018, The Central African Republic Diamond Database (2018) - Watersheds of Large Rivers: U.S. Geological Survey, Reston, VA.

    Online Links:

    This is part of the following larger work.

    DeWitt, Jessica D., Chirico, Peter G., Bergstresser, Sarah E., and Clark, Inga E., 2018, The Central African Republic Diamond Database – A Geodatabase of Archival Diamond Occurrences and Areas of Recent Artisanal and Small-scale Diamond Mining: U.S. Geological Survey, Reston, VA.

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: 14.721679683312
    East_Bounding_Coordinate: 27.202148432813
    North_Bounding_Coordinate: 10.746539462399
    South_Bounding_Coordinate: 2.8987157288129
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Calendar_Date: 2017
    Currentness_Reference:
    publication date
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: GIS dataset
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      Indirect_Spatial_Reference: This dataset covers the extent of the Central African Republic
      This is a Vector data set.
    2. What coordinate system is used to represent geographic features?
      The map projection used is Transverse Mercator.
      Projection parameters:
      Scale_Factor_at_Central_Meridian: 0.9996
      Longitude_of_Central_Meridian: 21.0
      Latitude_of_Projection_Origin: 0.0
      False_Easting: 500000.0
      False_Northing: 0.0
      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 30.0
      Ordinates (y-coordinates) are specified to the nearest 30.0
      Planar coordinates are specified in METERS
      The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.0.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    CAR_Watersheds_order6_streams
    Each row indicates a watershed polygon within Central African Republic (Source: All values in the dataset were calculated in ArcGIS 10.4)
    Area_km2
    Area of the watershed polygon in square kilometers (Source: Area value calculated by ArcGIS 10.4)
    Range of values
    Minimum:0.002192
    Maximum:17797.77362
    Units:square kilometers
    Shape_Length
    length of the perimeter of the watershed polygon, in meters (Source: Length value auto-calculated by ArcGIS 10.4)
    Range of values
    Minimum:237.992614
    Maximum:1492847.288358
    Units:meters
    Shape_Area
    Area of the watershed polygon in square meters (Source: Length value auto-calculated by ArcGIS 10.4)
    Range of values
    Minimum:2192.352385
    Maximum:17797773620.396732
    Units:square meters

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
  2. Who also contributed to the data set?
    U.S. Department of State, U.S. Agency for International Development
  3. To whom should users address questions about the data?
    Jessica D. DeWitt
    U.S. Geological Survey
    12201 Sunrise Valley Dr.
    Reston, VA
    USA

    703-648-6926 (voice)
    jdewitt@usgs.gov

Why was the data set created?

The purpose of this dataset is to delimit the watershed boundaries of large rivers in the Central African Republic.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 2017 (process 1 of 1)
    This watershed dataset was derived from the 30m Hydrologically Corrected Digital Elevation Model (DEM) of the Central African Republic using the tools in ArcGIS 10.4. In brief, this process entailed calculation of flow direction and flow accumulation grids from the DEM; classification of the flow accumulation grid into cells representing the location of a stream, resulting in a 'streams raster'; calculation of the Strahler Stream Order for the stream raster; reclassification of the stream grid to include only high order streams (orders 6-9); calculation of a stream link grid, which entailed enumeration of the reclassified stream's intersections; and calculation of watershed areas based on the stream link grid and the flow direction grid. Details regarding these procedures can be found in DeWitt and others (2017).
  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?
    No formal attribute accuracy tests were conducted
  2. How accurate are the geographic locations?
    No formal positional accuracy tests were conducted
  3. How accurate are the heights or depths?
    No formal positional accuracy tests were conducted
  4. Where are the gaps in the data? What is missing?
    Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details.
  5. How consistent are the relationships among the observations, including topology?
    No formal logical accuracy tests were conducted

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:
Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. The U.S. Geological Survey requests to be acknowledged as originator of these data in future products or derivative research.
  1. Who distributes the data set? (Distributor 1 of 1)
    Jessica D. DeWitt
    U.S. Geological Survey
    12201 Sunrise Valley Dr.
    Reston, VA
    USA

    703-648-6926 (voice)
    jdewitt@usgs.gov
  2. What's the catalog number I need to order this data set?
  3. What legal disclaimers am I supposed to read?
    Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. The U.S. Geological Survey requests to be acknowledged as originator of these data in future products or derivative research.
  4. How can I download or order the data?
  5. What hardware or software do I need in order to use the data set?
    This dataset is formatted as a feature class in an ESRI geodatabase. It requires the user to have geospatial software such as ESRI ArcGIS, Blue Marble Global Mapper, Que GIS, GRASS, or other GIS software.

Who wrote the metadata?

Dates:
Last modified: 05-Apr-2018
Metadata author:
Jessica D. DeWitt
U.S. Geological Survey
12201 Sunrise Valley Dr.
Reston, VA
USA

703-648-6926 (voice)
jdewitt@usgs.gov
Metadata standard:
Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Generated by mp version 2.9.47 on Thu Apr 5 06:55:52 2018