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Texas Digital Raster Graphics (DRGs)

DRG Metadata - Contains descriptive information about Digital Raster Graphics data (or Digital USGS Topographic Maps)
Sample Graphic

Table of Contents

The following text conforms with the hierarchy of data elements in the FGDC Content Standards for Digital Geospatial Metadata. This GIS layer supersedes all earlier copies, translations or coverages of the Air Quality Monitoring Stations coverage which may have been made by the Texas Commission on Environmental Quality (TCEQ).


1.1      Citation:
8.1         Originator: U.S. Geological Survey, EROS Data Center
8.2         Publication_Date: 1996-1997
8.4         Title: Digital Raster Graphics (DRGs)
8.6         Geospatial_Data_Presentation_Form: map
8.8         Publication_Information:
8.8.1          Publication_Place: Sioux Falls, SD  
8.8.2          Publisher: U.S. Geological Survey, EROS Data Center

1.2      Description:
1.2.1    Abstract: 
            The Texas Commission on Environmental Qaulity has
            acquired digital raster graphics (DRGs) from the U.S.
            Geological Survey for the entire state of Texas and some
            neighboring areas outside the state border. A DRG is a
            scanned image of a USGS topographic map, including all
            map collar information. The image inside the map neatline
            is georeferenced to the surface of the Earth. The DRGs
            available are of the 1:24,000, 1:100,000 and
            1:250,000-scale topographic map series.

            DRGs can be used to collect, review, and revise other
            digital data, especially digital line graphs (DLGs). When
            the DRG is combined with other digital products, such as
            digital orthophoto quadrangles (DOQs) or digital elevation
            models (DEMs), the resulting image provides additional
            visual information for the extraction and revision of base
            cartographic information.

1.2.2    Purpose: 
            For general purpose use, to be utilized by TCEQ staff and
            external customers.

            DRGs can be for validating digital line graphs (DLGs)
            and DLGS data collection and revision. DRGs can also help
            assess the completeness of digital data from other mapping
            agencies. They can be used to produce "hybrid" products,
            including combined DRGs and DOQs for revising and collecting
            digital data, DRGs and DEMs for creating shaded-relief DRGs,
            and combinations of DRG, DOQS, and DLGS data. Although a
            standard DRG is an effective mapping tool, its full potential
            for digital production is realized in combination with other
            digital data.

1.2.3    Supplemental_Information:
            Supplemental information about DRGs, including Standards for
            Digital Raster Graphics, can be obtained at
   Exit the TCEQ.
            The USGS documentation for DRGs can be obtained on-line
            at Exit the TCEQ.
            Metadata files can also be obtained from the original CDs
            housed at TNRIS. NOTE: Projection information for a specific
            DRG can be found in its individual metadata file.

            The DRG files available from TCEQ follow the USGS topographic
            map naming convention. In this convention:

               Characters 1-2 represent the southeast latitude of the
               one-degree area containing the DRG.

               Characters 3-5 represent the southeast longitude of the
               one-degree area containing the DRG.

               Characters 6-7 represent the USGS Map Index Number, a
               two-character alphanumeric code locating the quadrangle

               within the one-degree area. NOTE: Normally the alpha 
               character would be capitalized however due to a confirmed
               software bug in Arc/Info release 7.1.1, TCEQ has renamed
               all DRGs so that this character is lowercase.

            For example, the Pflugerville-W 7.5-minute DRG is named

1.3      Time_Period_of_Content: 
9.3         Range_of_Dates/Times:
9.3.1          Beginning_Date: Unknown
9.3.3          Ending_Date: Unknown
1.3.1    Currentness_Reference:
            USGS topographic maps are the source data for the DRGs.
            Exact dates of the source data can be obtained in the map
            collar information on the DRG.

1.4      Status:
1.4.1       Progress: Complete
1.4.2       Maintenance_and_Update_Frequency: As needed
1.5      Spatial_Domain: 
1.5.1       Bounding_Coordinates:        West_Bounding_Coordinate: -107        East_Bounding_Coordinate: -92        North_Bounding_Coordinate: 37        South_Bounding_Coordinate: 25

1.6      Keywords:
1.6.1       Theme:        Theme_Keyword_Thesaurus: None        Theme_Keyword: quads        Theme_Keyword: quadrangles        Theme_Keyword: 7.5'        Theme_Keyword: 7.5-minute        Theme_Keyword: 7.5 minute        Theme_Keyword: index        Theme_Keyword: topographic        Theme_Keyword: topo        Theme_Keyword: USGS topographic maps        Theme_Keyword: USGS topo maps        Theme_Keyword: USGS maps
1.6.2       Place:        Place_Keyword_Thesaurus: FIPS 5-2        Place_Keyword: TX

1.7      Access_Constraints: None

1.8      Use_Constraints: None

1.9      Point_of_Contact: 
10.1        Contact_Person_Primary:
10.1.1         Contact_Person: Greg Smithhart
10.1.2         Contact_Organization: TCEQ
10.4        Contact_Address:
10.4.1         Address_Type: Mailing address
10.4.2         Address: P.O. Box 13087 (Mail Code 197)
10.4.3         City: Austin
10.4.4         State_or_Province: TX
10.4.5         Postal_Code: 78711-3087
10.4.6         Country: USA
10.5        Contact_Voice_Telephone: 512-239-0859
10.7        Contact_Facsimile_Telephone: 512-239-0888
10.8        Contact_Electronic_Mail_Address: 

1.10     Browse_Graphic:
1.10.1      Browse_Graphic_File_Name: 
1.10.2      Browse_Graphic_File_Description: None.
1.10.3      Browse_Graphic_File_Type: GIF

1.11     Data_Set_Credit: USGS
1.13     Native_Data_Set_Environment: UNIX


2.1      Attribute_Accuracy:
2.1.1    Attribute_Accuracy_Report:
            The DRG uses a standard palette to ensure uniform color
            throughout a particular map series. The RGB values for a
            color, therefore, will remain consistent throughout that
            DRG series. Although the color values of the DRG may
            sometimes match those of the paper source map, a user will
            usually notice small differences between the colors on the
            digital image and on the paper map. Also, the quality of the
            user's monitor affects the DRG color displayed. Although
            the DRG generally contains the complete content of the
            source map, features may occasionally be blurred because of
            substandard source materials. The DRG also may contain
            misclassified pixels (color noise).

            The DRG is an 8-bit color image that employs a color palette
            to ensure uniform colors throughout a particular DRG series.
            All DRGs within a series must have the same RGB value.

2.2     Logical_Consistency_Report:
         The USGS DRG was produced with the intention of replicating
         as close as possible the original source map. Users of the
         DRG will note, however, that a certain amount of "noise" can
         be discerned when small areas are blown up or viewed under
         zoomed-in conditions. This noise is in the form of random
         specks or pixels of color and halos due to any number of
         factors, such as, the quality of the source, the use of
         screens and patterns on the litho, and the unevenness of ink
         due to saturation and absorption. Discontinuities or breaks
         in linear features may also be present and are due to improper
         calibration or usage of the scanner, the condition of the
         source, and resampling. Descreening, quantizing, and noise
         filtering are methods used to reduce noise, which, besides
         creating a more aesthetically pleasing image, have the added
         benefit of reducing the size of the image file. Removal of
         lithographic screen patterns is preferred but not required.

2.3   Completeness_Report: 
         Image completeness was checked by visually inspecting a sampling
         of DRGs. Each selected DRG was examined for gaps (missing data)
         in the main body of the map, the map collar, the over-edge areas,
         and any insets.

2.4      Positional_Accuracy:  
2.4.1       Horizontal_Positional_Accuracy:     Horizontal_Positional_Accuracy_Report:
               Random samplings of DRGs were accuracy tested by USGS
               and/or the originator of the data. The accuracy test
               was performed by comparing the positions of UTM grid
               intersections against the corresponding location on the
               digital image. A visual inspection determined whether
               those coordinates fell within the pixels that define a
               grid tick. DRGs duplicate the horizontal accuracy of 
               their source.

               In addition, a stratified random sample of DRGs were
               accuracy-tested by TCEQ GIS Section staff members.
               Individual quadrangle polygons were mathematically
               generated and then projected using an AML program. These
               polygons were then overlaid with the respective DRG.
               The maximum offset was measured at a zoom ratio of 1:1.
               The error ranged from 2 meters to 13 meters.        Quantitative_Horizontal_Positional_Accuracy_Assessment:         Horizontal_Positional_Accuracy_Value:0         Horizontal_Positional_Accuracy_Explanation: 
                      DRGs will retain the horizontal accuracy of the
                      source maps. Most USGS printed maps contain the
                      National Map Accuracy Standards (NMAS) note in
                      the collar area. The NMAS states that for maps on
                      publication scales of 1:20,000 or smaller, not more
                      than 10% of the points tested shall be in error by
                      more than 1/50 inch measured on the publication scale.
                      Test points must be "well defined", that is, easily
                      visible or recoverable on the ground. For DRGs this
                      accuracy statement applies only to the area of the
                      DRG that falls within the neatline of the source map
                      (excluding inset areas). Over-edge areas falling
                      outside the transformation boundary area (the map
                      neatline), can exhibit anomalies or discrepancies.
                      These anomalies will also appear in the map inset
                      areas and in the map collar. For maps without the
                      NMAS note, the horizontal accuracy is unknown.
                      However, the DRG will retain the accuracy of the
                      source map.

2.5      Lineage:
2.5.1       Source_Information:        Source_Citation:
8.1               Originator: U.S. Geological Survey, EROS Data Center
8.2               Publication_Date: 1996-1997
8.4               Title: Digital Raster Graphics (DRGs)
8.8               Publication_Information:
8.8.1                Publication_Place: Sioux Falls, SD
8.8.2                Publisher: U.S. Geological Survey, EROS Data Center        Source_Scale_Denominator: 24000        Type_of_Source_Media: paper        Source_Time_Period_of_Content:         Source_Currentness_Reference: publication date        Source_Citation_Abbreviation: USGS Topo        Source_Contribution:
                  The standard area of coverage of a DRG is the entire area
                   printed on a USGS topographic map including the map collar,
                   any over-edge areas, and insets.
2.5.2       Process_Step:        Process_Description:
               A detailed description of USGS DRG processing and process
               contact information can be obtained at
      Exit the TCEQ.
               DRGs were copied from the original CDs received from USGS
               at TCEQ. The original CDs were delivered to TNRIS.
               A program was run to drop the first character (known as 
               "Category" in USGS's DRG file naming convention) from each
               DRG's image (.TIF) and world (.TFW) files for consistency
               purposes; the USGS DEMs are named in this manner. Information
               on USGS's DRG naming convention can be found at
      the TCEQ.


3.2      Direct_Spatial_Reference_Method: Raster
3.4      Raster_Object_Information:
3.4.1       Raster_Object_Type: Pixel


4.1      Horizontal_Coordinate_System_Definition:
4.1.2       Planar:        Map_Projection:         Map Projection Name: Transverse_Mercator        Grid_Coordinate_System:         Grid Coordinate System Name: Universal Transverse Mercator         Universal_Transverse_Mercator:           UTM Zone Number: 13,14,15
4.1.4       Geodetic_Model:        Horizontal_Datum_Name: The datum used is the datum of the 
               DRG source (e.g. NAD27, NAD83).        Ellipsoid_Name: The ellipsoid used is the ellipsoid of the
               DRG source (e.g. Clarke 1866, GRS 1980)


5.2      Overview Description:
5.2.1       Entity_and_Attribute_Overview:
            Each raster entity or pixel contains a digital number from 0
            through 12 referencing a color palette of RGB values from 0
            through 255 in which the standard colors used in the DRG are
            defined. 5.2.2       Entity_and_Attribute_Detail_Citation:
            USGS National Mapping Program Technical Instructions
            Standards for Digital Raster Graphics


6.1      Distributor: 
10.1        Contact_Person_Primary: Greg Smithhart
10.2        Contact_Organization_Primary: TCEQ
10.4        Contact_Address: 
10.4.1         Address_Type: mailing address
10.4.2         Address: P. O. Box 13087 (Mail Code 197)
10.4.3         City: Austin
10.4.4         State_or_Province: TX
10.4.5         Postal_Code: 78711-3087
10.4.6         Country: USA
10.5        Contact_Voice_Telephone: 512-239-0859
10.7        Contact_Facsimile_Telephone: 512-239-0888
10.8        Contact_Electronic_Mail_Address:   

6.2      Resource_Description: TCEQ Certified Base Map Layers

6.3      Distribution_Liability: 
         Although these data have been processed successfully on a
         computer system at the USGS, no warranty expressed or implied
         is made by the USGS or TCEQ regarding the utility of the data
         on any other system, nor does the act of distribution constitute
         any such warranty.

6.4      Standard_Order_Process:
6.4.2       Digital_Form:        Digital_Transfer_Information:         Format_Name: Tagged Image File Format (TIFF)         Format_Version_Number: 6.0         Format_Version_Date:         Format_Specification:
                  Links to GeoTiff and TIFF 6.0 format specifications can
                  be found here Exit the TCEQ.         Format_Information_Content:

                  To facilitate file manipulation by the widest possible
                  range of potential users, data and text files conform
                  to the USGS topographic map naming convention. The
                  associated DRG image (.TIF), world (.TFW), and metadata
                  (.FGD) files incorporate an intelligent data set name
                  consisting of descriptive metadata wrapped around a
                  standardized kernel that describes the spatial location
                  of the file. The intent of this file naming protocol is
                  to positively identify the spatial identity of the file.         File_Decompression_Technique: PackBits         Transfer_Size: 2 MB to 25 MB        Digital_Transfer_Option:         Online_Option:          Computer_Contact_Information: World Wide Web           Network_Address:            Network_Resource_Name:

6.7      Available_Time_Period: Immediate


7.1      Metadata_Date: 19980309
7.2      Metadata_Review_Date: 19980309
7.3      Metadata_Future_Review_Date: Unknown
7.4      Metadata_Contact: 
10.1        Contact_Person_Primary: Greg Smithhart
10.2        Contact_Organization_Primary: TCEQ
10.4        Contact_Address: 
10.4.1         Address_Type: mailing address
10.4.2         Address: P. O. Box 13087 (Mail Code 197)
10.4.3         City: Austin
10.4.4         State_or_Province: TX
10.4.5         Postal_Code: 78711-3087
10.4.6         Country: USA
10.5        Contact_Voice_Telephone: 512-239-3850
10.7        Contact_Facsimile_Telephone: 512-239-0888
10.8        Contact_Electronic_Mail_Address: 

7.5      Metadata_Standard_Name: 
         FGDC Content Standards for Digital Geospatial Metadata

7.6      Metadata_Standard_Version: 19940608

7.7      Metadata_Time_Convention: Local Time

7.8      Metadata_Access_Constaints: None

7.9      Metadata_Use_Constaints: None

7.10     Metadata_Security_Information:
            Metadata_Security_Classification_System: None
            Metadata_Security_Classification: Unclassified