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Water: BASINS

Metadata (DEM)

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USGS 300 Meter Resolution, 1-Degree Digital Elevation Models (DEM) for CONUS, Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands


 

Identification_Information:

Citation:
Citation_Information:
Originator: U.S. Environmental Protection Agency/Office of Water/OST Basins
Publication_Date: 20070611
Title:
USGS 300 Meter Resolution, 1-Degree Digital Elevation Models (DEM) for CONUS, Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands
Publication_Information:
Publication_Place: Washington DC
Publisher: US EPA/Office of Water
Online_Linkage:
For BASINS model and hydrographic data http://www.epa.gov/waterscience/BASINS/
For original metadata and documentation of source data
Description:
Abstract:
Digital Elevation Model (DEM) is the terminology adopted by the USGS to describe terrain elevation data sets in a digital raster form. The standard DEM consists of a regular array of elevations cast on a designated coordinate projection system. 1-degree DEMs (3- by 3-arc second data spacing) provides coverage in 1- by 1-degree blocks. The basic elevation model is produced by or for the Defense Mapping Agency (DMA), but is distributed by the USGS in the DEM data record format. Coverage is for the United States.

The US EPA 1-degree DEM shapefiles are polygonal representations of the original USGS DEM raster files resampled to a 300m x 300m cell size. Catolog Units (CU)in each of the ten US EPA Regions were buffered by a two mile distance. The buffered CUs were used to clip corresponding areas from the DEM raster files. The resulting files were output in Environmental Systems Research Institute's (ESRI) shapefile format. Two attribute fields were added to each shapefile's database component to represent elevation in both meters and feet.


Purpose:
DEM's can be used as source elevation data for digital orthophotos, and, as layers in geographic information systems, for earth science analysis. DEM's can also serve as tools for volumetric analysis, for site location of towers, or for drainage basin delineation. The ESRI shapefile format allows for analysis involving elevational data and also provides for the possibility of contour generation.
Supplemental_Information:
One degree DEM's have rows and columns which are based on the geographic coordinate system. The use of this system results in a rectangular DEM which shares a common edge and therefore duplicate points with other adjacent 1-degree DEM's.

The original USGS DEMs were downloaded and imported into ArcInfo grid format using the demlattice command. An Arc Macro Language (AML) procedure was used to create Arcview shapefiles for each CU in the United States. Processing started with generating a list of CUs in an EPA Region and reading the list into ArcInfo. For each CU in the list, an ArcInfo coverage was generated by reselecting all polygons associated with the CU from a nationwide CU coverage. The individual CU polygon coverage was then buffered with a two mile buffer distance. The buffered coverage was overlayed onto an index coverage of 1:250,000 scale DEMs for the United States. A list was generated of all the DEMs that the buffered coverage touched on the index. Each DEM grid coverage in the resulting list was then mosaiced into a single grid coverage. This single grid coverage was then projected from a geographic-decimal degrees to an albers-meters projection. The single grid coverage is resampled to a 300 meter x 300 meter cell size and converted from a raster coverage to a vector polygon coverage. The polygon grid coverage was clipped by the buffered CU coverage and projected back to geographic-decimal degrees. Polygons were built for the clipped DEM grid coverage and an ArcView shapefile built. Once the shapefile was built, the database component was modified to include fields for elevation in both meters and feet.

Converting the original 1-degree DEMs into ESRI shapefile format reduced the number of cells in each DEM coverage by unioning adjacent polygons with the same elevation.

DEM files for Alaska, Puerto Rico, and the U.S. Virgin Islands would not initially import into ArcInfo. ArcInfo versions below 7.1.2 have a bug in the DEMLATTICE command that incorrectly reads the accuracy code found in the first line of the file. This code needs to be changed to 0 from the original codes of either 2231 or 2232. The changes were made by changing the block size of the file. The command line for this step is:

dd if=file.dem of=file.var ibs=4096 cbs=1024 conv=unblock.

The first line of code was then edited to change the accuracy code. This step is done by replacing the each character of 223 with a space and the final character of the four digit code with a zero.

Reviews_Applied_To_Data Upon completion of processing, each CU shapefile was viewed in an ArcView project to verify the completeness of the datafiles, to look for holes in the data, and to look for spikes in the data. Individual polygons were measured to verify the 300 meter x 300 meter cell size. Additionally, a coverage of all CUs in the US EPA Region was drawn on top of the 1-degree DEM shapefiles to verify that each CU was processed.

References_Cited U.S. Geological Survey, 1993, Digital Elevation Models-Data Users Guide 5, National Mapping Program, USGS, Reston, Virginia  Exit EPA Disclaimer

U.S. Geological Survey, 1995, Metadata for 1-degree Digital Elevation Models. U.S. Geological Survey, Reston, Virginia. and  Exit EPA Disclaimer


Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 19791000
Ending_Date: 19900401
Currentness_Reference: Publication date
Status:
Progress: Complete
Maintenance_and_Update_Frequency: Irregular
Spatial_Domain:
Bounding_Coordinates:
West_Bounding_Coordinate: -170.0000
East_Bounding_Coordinate: -65.0000
North_Bounding_Coordinate: 70.0000
South_Bounding_Coordinate: 17.0000
Keywords:
Theme:
Theme_Keyword_Thesaurus: none
Theme_Keyword: DEM
Theme_Keyword: digital elevation model
Theme_Keyword: digital terrain model
Theme_Keyword: hypsography
Theme_Keyword: altitude
Theme_Keyword: height
Theme_Keyword: contour line
Theme_Keyword: digital contours
Theme_Keyword: shapefile
Place:
Place_Keyword_Thesaurus: Geographic Names Information System
Place_Keyword: Conterminous United States of America
Place_Keyword: Puerto Rico PR
Place_Keyword: U.S. Virgin Islands VI
Place_Keyword: Alabama AL
Place_Keyword: Alaska AK
Place_Keyword: Arizona AZ
Place_Keyword: Arkansas AR
Place_Keyword: California CA
Place_Keyword: Colorado CO
Place_Keyword: Connecticut CT
Place_Keyword: Delaware DE
Place_Keyword: District of Columbia DC
Place_Keyword: Florida FL
Place_Keyword: Georgia GA
Place_Keyword: Hawaii HI
Place_Keyword: Idaho ID
Place_Keyword: Illinois IL
Place_Keyword: Indiana IN
Place_Keyword: Iowa IA
Place_Keyword: Kansas KS
Place_Keyword: Kentucky KY
Place_Keyword: Louisiana LA
Place_Keyword: Maine ME
Place_Keyword: Maryland MD
Place_Keyword: Massachusetts MA
Place_Keyword: Michigan MI
Place_Keyword: Minnesota MN
Place_Keyword: Mississippi MS
Place_Keyword: Missouri MO
Place_Keyword: Montana MT
Place_Keyword: Nebraska NE
Place_Keyword: Nevada NV
Place_Keyword: New Hampshire NH
Place_Keyword: New Jersey NJ
Place_Keyword: New Mexico NM
Place_Keyword: New York NY
Place_Keyword: North Carolina NC
Place_Keyword: North Dakota ND
Place_Keyword: Ohio OH
Place_Keyword: Oklahoma OK
Place_Keyword: Oregon OR
Place_Keyword: Pennsylvania PA
Place_Keyword: Rhode Island RI
Place_Keyword: South Carolina SC
Place_Keyword: South Dakota SD
Place_Keyword: Tennessee TN
Place_Keyword: Texas TX
Place_Keyword: Utah UT
Place_Keyword: Vermont VT
Place_Keyword: Virginia VA
Place_Keyword: Washington WA
Place_Keyword: West Virginia WV
Place_Keyword: Wisconsin WI
Place_Keyword: Wyoming WY

Access_Constraints: None
Use_Constraints: None

Security_Information:
Security_Classification_System: None
Security_Classification: UNCLASSIFIED
Security_Handling_Description: None

Native_Data_Set_Environment: ArcView 3.x shapefiles on Windows 95 PC



 

Data_Quality_Information:



Attribute_Accuracy:
Attribute_Accuracy_Report:
The accuracy of a DEM is dependent upon the level of detail of the source and the grid spacing used to sample that source. The primary limiting factor for the level of detail of the source is the scale of the source materials. The proper selection of grid spacing determines the level of content that may be extracted from a given source during digitization.
Logical_Consistency_Report:
The fidelity of the relationships encoded in the data structure of the DEM are automatically verified using a USGS software program upon completion of the data production cycle. The test verifies full compliance to the DEM specification
Completeness_Report:
The DEM is visually inspected for completeness on a DEM view and edit system for the purpose of performing a final quality control and if necessary edit of the DEM. The physical format of each digital elevation model is validated for content completeness and logical consistency during production quality control and prior to archiving in the National Digital Cartographic Data Base. Level 2 DEM: Level 2 DEM's may contain void areas due to interruptions to contours in the source graphic or DLG. Void area elevation grid posts are assigned the value of -32,767. In addition, suspect elevation areas may exist in the DEM but are not specifically identified. Suspect areas can be located on the source graphic as a "disturbed surface" which are symbolized by contours overprinted with photorevised or other surface patterns.
Positional_Accuracy:
Horizontal_Positional_Accuracy:
Horizontal_Positional_Accuracy_Report:
Digital elevation models meet horizontal National Map Accuracy Standards (NMAS) accuracy requirements. NMAS horizontal accuracy requires that at least 90 percent of points tested are within 0.02 inches of the true position. The primary reference from which 1-degree DEM accuracy is derived is source-based, as a minimum, meeting NMAS For 100,000-scale USGS topographic series maps.
Quantitative_Horizontal_Positional_Accuracy_Assessment:
Horizontal_Positional_Accuracy_Value: 300
Horizontal_Positional_Accuracy_Explanation:
Digital elevation models meet horizontal National Map Accuracy Standards (NMAS) accuracy requirements. RMSE of the DEM. The 1-degree DEM accuracy is source-dependent and is based on the 1:100,000-scale USGS topographic series map.
Vertical_Positional_Accuracy:
Vertical_Positional_Accuracy_Report:
The vertical root-mean-square error (RMSE) statistic is used to describe the vertical accuracy of a DEM, encompassing both random and systematic errors introduced during production of the data. The RMSE is encoded in element number 5 of record C of the DEM. Accuracy is computed by a comparison of linear interpolated elevations in the DEM with corresponding known elevations. Test points are well distributed, representative of the terrain, and have true elevations with accuracies well within the DEM accuracy criteria. Acceptable test points include, in order of preference: field control, aerotriangulated test points, spot elevations, or points on contours from existing source maps with appropriate contour interval. A minimum of 28 test points per DEM is required to compute the RMSE, which is composed of a single test using 20 interior points and 8 edge points. Edge points are those which are located along, at, or near the quadrangle neatlines and are deemed by the editor to be useful to evaluating the accuracy of the edge of the DEM. Collection of test point data and comparison of the DEM with the quadrangle hypsography are conducted by the quality control units within the USGS. There are three types of DEM vertical error; blunder, systematic and random. These errors are reduced in magnitude by editing but cannot be completely eliminated and may be encountered.

Blunder errors are those errors of major proportions and are easily identified and removed during interactive editing. Systematic errors are those errors that follow some fixed pattern and are introduced by data collection procedures and systems. These error artifacts include: vertical elevation shifts, misinterpretation of terrain surface due to trees, buildings and shadows, and fictitious ridges, tops, benches or striations. Random errors result from unknown or accidental causes. DEMs are edited to correctly depict elevation surfaces that correspond to water bodies of specified size.

Level 2 DEM: A vertical RMSE of one-half of the contour interval (of 100,000-scale source), determined by the source map, is the maximum permitted. Systematic errors may not exceed one contour interval, determined by the source map, is the maximum permitted. Systematic errors may not exceed one contour interval specified by the source graphic. Level 2 DEM's have been processed or smoothed for consistency and edited to remove identifiable systematic errors.



Lineage:


Process_Step:
Process_Description:
Example of the GIS process for the DEM convertion to shapefiles

PROJECT COVER DEMCLIPPED OUTCOV BUILD OUTCOV POLY IMPORT COVER outcov.E00 outcov

Process_Date: 20070611


 

Spatial_Reference_Information:

Horizontal_Coordinate_System_Definition:
Geographic:
Latitude_Resolution: 0.0001
Longitude_Resolution: 0.0001
Geographic_Coordinate_Units: Decimal Degrees
Geodetic_Model:
Horizontal_Datum_Name: North American Datum of 1983
Ellipsoid_Name: Geodetic Reference System 80
Semi-major_Axis: 6,378,137
Denominator_of_Flattening_Ratio: 298.257
Vertical_Coordinate_System_Definition:
Altitude_System_Definition:
Altitude_Datum_Name: National Geodetic Vertical Datum of 1929
Altitude_Resolution: 1
Altitude_Distance_Units: meters
Altitude_Encoding_Method:
Explicit elevation coordinate included with horizontal coordinates

 

Entity_and_Attribute_Information:

Detailed_Description:
Entity_Type:
Entity_Type_Label: DEM.SHP
Entity_Type_Definition: DEM shapefile
Entity_Type_Definition_Source: USEPA/OW
Attribute:
Attribute_Label: ELEV_M
Attribute_Definition: Elevation in meters
Attribute_Definition_Source: Generated during ArcInfo processing
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: Integer
Enumerated_Domain_Value_Definition: 8 11 F 0
Enumerated_Domain_Value_Definition_Source: USEPA/OW
Attribute:
Attribute_Label: ELEV_FT
Attribute_Definition: Elevation in feet
Attribute_Definition_Source: Generated during ArcInfo processing
Attribute_Domain_Values:
Enumerated_Domain:
Enumerated_Domain_Value: Integer
Enumerated_Domain_Value_Definition: 8 11 F 0
Enumerated_Domain_Value_Definition_Source: USEPA/OW

 

Distribution_Information:


Distributor:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USEPA Office of Water/OST Basins
Contact_Address:
Address_Type: mailing address
Address: 1200 Pennsylvania Ave., NW (4305T)
City: Washington
State_or_Province: District of Columbia
Postal_Code: 20460
Contact_Voice_Telephone: 202-566-0400
Contact_Facsimile_Telephone: 202-566-0409
Contact_Electronic_Mail_Address: basins@epa.gov
Hours_of_Service: 9-3 EST
Distribution_Liability:
Although these data have been processed successfully on a computer system under contract to the U.S. Environmental Protection Agency (USEPA), no warranty expressed or implied is made by the USEPA regarding the utility of the data on any other system, nor shall the act of distribution constitute any such warranty. The USEPA will warrant the delivery of this product in computer-readable format.
Standard_Order_Process:
Digital_Form:
Digital_Transfer_Information:
Format_Name:
Environmental Systems Research Institute (ESRI) ArcView Shapefile
Digital_Transfer_Option:
Online_Option:
Computer_Contact_Information:
Network_Address:
Network_Resource_Name:
Offline_Option:
Offline_Media: CD-ROM
Recording_Format: ISO 9660
Fees: None
Ordering_Instructions:
When requesting data by phone or mail, please inquire about spatial data sets that work with Better Assessment Science Integrating Point and Nonpoint Sources (BASINS). The BASINS web page has instructions for downloading datasets. It also has a link to The National Center for Environmental Publications and Information (NCEPI), from which BASINS CD-ROMs may be ordered. Each CD-ROM contains the BASINS v2.0 Application and this data set along with others covering the spatial extent of an EPA Region.

 

Metadata_Reference_Information:

Metadata_Date: 20070611
Metadata_Contact:
Contact_Information:
Contact_Organization_Primary:
Contact_Organization: USEPA Office of Water/waterscience/SASD Basins
Contact_Address:
Address_Type: mailing address
Address: 1200 Pennsylvania Ave., NW (4305T)
City: Washington
State_or_Province: District of Columbia
Postal_Code: 20460
Contact_Voice_Telephone: 202-566-0400
Contact_Facsimile_Telephone: 202-566-0409
Contact_Electronic_Mail_Address: basins@epa.gov
Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata
Metadata_Standard_Version: 19940608


Generated by mp on Wed Aug 26 10:09:45 1998
Text Version


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