USGS 7.5 minute (10 Meter) Digital Elevation Models (DEM's)


Originator: Washington State Geospatial Data Archive (WAGDA)
Publication_Date: 19980218
Title: USGS 7.5 minute (10 Meter) Digital Elevation Models (DEM's)
Geospatial_Data_Presentation_Form: map
Publication_Place: Seattle, WA
Publisher: Washington State Geospatial Data Archive
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. The DEM data are stored as a series of profiles in which the spacing of the elevations along and between each profile is in regular whole number intervals. The normal orientation of data is by columns and rows. Each column contains a series of elevations ordered from south to north with the order of the columns from west to east. The DEM is formatted as one ASCII header record (A- record), followed by a series of profile records (B- records) each of which include a short B-record header followed by a series of ASCII integer elevations per each profile. The last physical record of the DEM is an accuracy record (C-record).

7.5-minute DEM (10- by 10-m data spacing, cast on Universal Transverse Mercator (UTM) projection). Provides coverage in 7.5- by 7.5-minute blocks. Each product provides the same coverage as a standard USGS 7.5-minute quadrangle without over edge. Coverage is for Southwestern Washington up through part of the Puget Sound Basin.

DEM's can be used as source 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. These data were collected as part of the National Mapping Program.
7.5-minute DEMs have rows and columns which vary in length and are staggered. The UTM bounding coordinates form a quadrilateral (no two sides are parallel to each other), rather than a rectangle. The user will need to pad out the uneven rows and columns with blanks or flagged data values, if a rectangle is required for the user's application. Some software vendors have incorporated this function into their software for input of standard formatted USGS DEMs.
Calendar_Date: 19950101
Currentness_Reference: ground condition
Progress: Complete
Maintenance_and_Update_Frequency: Irregular
West_Bounding_Coordinate: -124
East_Bounding_Coordinate: -121.25
North_Bounding_Coordinate: 48.45
South_Bounding_Coordinate: 45.3
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
U.S. Department of Commerce, 1977, Countries, dependencies, areas of special sovereignty, and their principal administrative divisions (Federal Information Processing Standard 10-3):Washington, D.C., National Institute of Standards and Technology.
Place_Keyword: US
Place_Keyword: WA
Access_Constraints: None
Use_Constraints: None.
Contact_Person: GIS Librarian
Contact_Organization: University of Washington Libraries
Contact_Position: GIS Librarian
Address_Type: mailing address
Address: Box 352900
City: Seattle
State_or_Province: WA
Postal_Code: 98195-2900
Country: US
Contact_Voice_Telephone: 206-543-9392
Contact_Facsimile_Telephone: 206-685-8049
Sample 1:24,000 Digital Elevation Models, Maple Valley Quadrangle, Hillshade
Browse_Graphic_File_Type: GIF
US Geological Survey. Acknowledgement of WAGDA and the U.S. Geological Survey would be appreciated in products derived from these data.
Native_Data_Set_Environment: Windows_NT, 4.0, Intel UNIX, ARC/INFO version 7.1

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 thatmay be extracted from a given source during digitization. 10 Meter sampling, from 1:24k USGS quad sheets.
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.
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. Due to the variable orientation of the quadrilateral in relation to the Universal Transverse Mercator (UTM) projection grid, profiles that pass within the bounds of the DEM quadrilateral, may be void of elevation grid points, and are not represented in the DEM. This condition occurs infrequently and is always the first or last profile of the dataset. 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, " symbolized by contours overprinted with photorevised or other surface patterns.
The horizontal accuracy of the DEM is expressed as an estimated root mean square error (RMSE). The estimate of the RMSE is based upon horizontal accuracy tests of the DEM source materials which are selected as equal to or less than intended horizontal RMSE error of the DEM. The testing of horizontal accuracy of the source materials isaccomplished by comparing the planimetric (X and Y) coordinates of well-defined ground points with the coordinates of the same points as determined from a source of higher accuracy.
The vertical 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 errors; blunder, systematic and random. These errors are reduced in magnitude by editing but cannot be completely eliminated. 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.

DEM's 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, 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 DEMs have been processed or smoothed for consistency and edited to remove identifiable systematic errors.

Originator: U.S. Geological Survey
Publication_Date: Unknown
Title: USGS digital contour lines
Geospatial_Data_Presentation_Form: map
Publication_Place: Reston, VA
Publisher: U.S. Geological Survey
Title: USGS 7.5 minute (10 Meter) Digital Elevation Models (DEM's)
Type_of_Source_Media: physical drive
Calendar_Date: 19950101
Source_Currentness_Reference: ground condition
Source_Citation_Abbreviation: CIT19
hypsographic vector information which is interpolated to regular grid posts to form DEM grids in 30- by 30- meter UTM data spacing within the 7.5 minute DEM bounds.
The production procedures, instrumentation, hardware and software used in the collection of standard U. S. Geological Survey (USGS) Digital Elevation Models (DEM's) vary depending on systems used at the contractor, cooperator or National Mapping Division (NMD) production sites. This process step describes, in general, the process used in the production of standard USGS DEM datasets.

Level 2 DEM: Level 2 DEM's are produced by converting 1:24,000-scale and 1:100,000-scale hypsography digital line graph (DLG) data to DEM format or the DEM's are generated from vector data derived from scanned raster files of USGS 1:24.000-scale or 1:100,000-scale map series contour separates.

Water body editing: DEM surface areas corresponding to water bodies are flattened and assigned map specified or estimated surface elevations. Water body areas are defined as ponds, lakes, and reservoirs that exceed 0.5 inches at map scale and double line drainage that exceeds 0.25 inches at map scale. Water body shorelines are derived either from a hypsographic DLG or by interactive delineation from 1:24,000- scale or 1:100,000-scale USGS map series.

Edge matching: DEM datasets within a project area (consisting of a number of adjacent files) are edge matched to assure terrain surface continuity between files. Edge matching is the process of correcting adjacent elevation values along common edges. The objective of edge matching is to create more accurate terrain representations by correcting the alignment of ridges and drains, and overall topographic shaping within an approximately 25-30 row or column grid post zone on both edges.

Quality control: DEM's are viewed on interactive editing systems to identify and correct blunder and systematic errors. DEM's are verified for physical format and logical consistency at the production centers and before archiving in the National Digital Cartographic Data Base (NDCDB) utilizing the Digital Elevation Model Verification System (DVS) software.

Import USGS DEM format into Arc/INFO using DEMLATTICE command.

Export Arc/INFO lattice to a BIL image file and compressed for distribution.

Process_Date: ? To 19971029

Direct_Spatial_Reference_Method: Raster
Raster_Object_Type: Grid Cell
Row_Count: 1400
Column_Count: 959

Grid_Coordinate_System_Name: Universal Transverse Mercator
UTM_Zone_Number: 10
Scale_Factor_at_Central_Meridian: 9996
Longitude_of_Central_Meridian: -123 00 00
Latitude_of_Projection_Origin: 0 0
False_Easting: 500000
False_Northing: 0 0
Planar_Coordinate_Encoding_Method: Coordinate Pair
Abscissa_Resolution: 30
Ordinate_Resolution: 30
Planar_Distance_Units: meters
Horizontal_Datum_Name: HPGN
Ellipsoid_Name: GRS1980
Semi-major_Axis: 6378206.4
Denominator_of_Flattening_Ratio: 294.98

The digital elevation model is composed of a 6- character integer raster representing a gridded form of a topographic map hypsography overlay. Each raster entity contains a 6-character integer value between -32,767 to 32,768.
U.S.Department of the Interior, U.S. Geological Survey, Digital Elevation Models -- Data Users Guide; Reston, VA.

A hypertext extract is available at: <URL:>

Softcopies in ASCII and WordPerfect format are available at: <URL:>

U.S.Department of the Interior, U.S. Geological Survey, 1992, Standards for digital elevation models: Reston, VA,

Softcopies in ASCII and WordPerfect format are available at: <URL:>

Contact_Organization: University of Washington Libraries GIS
Contact_Position: Washington State Geospatial Data Archive Administrator
Address_Type: mailing address
Address: Box 352900
City: Seattle
State_or_Province: WA
Postal_Code: 98195-2900
Country: US
Contact_Voice_Telephone: 206-543-9392
Contact_Facsimile_Telephone: 206-685-8049
WAGDA provides these geographic data "as is." WAGDA makes no guarantee or warranty concerning the accuracy of information contained in the geographic data. WAGDA further makes no warranties, either expressed or implied as to any other matter whatsoever, including, without limitation, the condition of the product, or its fitness for any particular purpose. The burden for determining fitness for use lies entirely with the user. Although these data have been processed successfully on computers of WAGDA, no warranty, expressed or implied, is made by WAGDA regarding the use of these data on any other system, nor does the fact of distribution constitute or imply any such warranty.

In no event shall the WAGDA have any liability whatsoever for payment of any consequential, incidental, indirect, special, or tort damages of any kind, including, but not limited to, any loss of profits arising out of use of or reliance on the geographic data or arising out of the delivery, installation, operation, or support by WAGDA.

Metadata_Date: 19980228
Metadata_Review_Date: 19980225
Metadata_Future_Review_Date: none
Contact_Organization: University of Washington Libraries GIS
Contact_Position: Washington State Geospatial Data Archive Administrator
Address_Type: mailing address
Address: Box 352900
City: Seattle
State_or_Province: WA
Postal_Code: 98195-2900
Country: US
Contact_Voice_Telephone: 206-543-9392
Contact_Facsimile_Telephone: 206-685-8049
Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata
Metadata_Standard_Version: Version of June 8, 1994
Metadata_Access_Constraints: none
Metadata_Use_Constraints: none

Generated by mp on Tue Nov 3 12:37:25 1998