New York State Digital Elevation Models


Originator: U.S. Geological Survey
Publication_Date: Unknown
Publication_Time: Unknown
Title: New York State Digital Elevation Models
Publication_Place: Reston, VA
Publisher: U.S. Geological Survey
Online_Linkage: <>
A digital Elevation Model (DEM) 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). The 7.5-minute DEM (10- by 10-m data spacing) is cast on the Universal Transverse Mercator (UTM) projection (the quads UTM zone can be found in the header record(Record A)) in the North American Datum of 1927. It provides coverage in 7.5- by 7.5-minute blocks. Each product provides the same coverage as a standard USGS 7.5-minute quadrangle, but overedges are published as separate DEM files. Coverage is available for all quads completely contained within New York State, plus some additional ones falling along the borders and containing significant area of the State's land.
DEMs can be used as source data for digital orthophotos and as layers in geographic information systems for earth science analysis. DEMs can also serve as tools for volumetric analysis, for site location of towers, or for drainage basin delineation. These data are 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: Unknown
Currentness_Reference: Ground Condition
Progress: Complete
Maintenance_and_Update_Frequency: Irregular
West_Bounding_Coordinate: -074.235500
East_Bounding_Coordinate: -073.702900
North_Bounding_Coordinate: +42.815300
South_Bounding_Coordinate: +42.421500
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: landforms
Theme_Keyword: relief
Theme_Keyword: topography
Theme_Keyword: cartography
Theme_Keyword: digital mapping
Theme_Keyword: hydrography
Theme_Keyword: mapping
Theme_Keyword: raster
Theme_Keyword: grid
Theme_Keyword: cell
Theme_Keyword: NYSDEC
Department of Commerce, 1987, Codes for the Identification of the States, The District of Columbia and the Outlying Areas of the U.S., and Associated Areas (Federal Information Processing Standard 5-2): Washington, Department of Commerce, National Institute of Standards and Technology
Place_Keyword: US
Place_Keyword: NY
Place_Keyword: New York State
Access_Constraints: None
Only that acknowledgement of the U.S. Geological Survey and NYSDEC would be apprecieated in products derived from these data.
Contact_Person: Ricardo Lopez-Torrijos
Contact_Organization: New York State Department of Environmental Conservation
Address_Type: mailing and physical address
Address: 50 Wolf Rd
City: Albany
State_or_Province: New York
Postal_Code: 12233-3507
Contact_Voice_Telephone: 518-457-0726
24,000 scale hypsographic contour linework drawn by photogrametric, plane table or other methods by USGS, US Army Corp of Engineers, Tennesy Valley Authority or others. Linework copied onto stable-base mylar. Raster image of linework created by USGS, Reston, with Optronics drum scanner at an aperture of 20um, to give an equivalent resolution of 1024 DPI. Raster data converted to vector with line-center algorithm in LT4X v. 3.1, 11/11/93, by John Dabritz of Infotec Development Inc. Grid elevations calculated with 8-profile weighted linear interpolation, with cubic smoothing of slope at the contour line as per algorithm in above mentioned LT4X v. - export in DEM format, UTM meters, - grid height and width of 10 mt, - clipping (overedge) coordinate in UTM mt, - input coord feet or meters (depending on source material), output in meters/decimeters, - DEM grid points which are on a profile section longer than 80 mt are smoothed by passing the grid through a low pass-filter twice. The filter size (see below) is of 9 cell diameters (aprox 9 mt). The purpouse here is to leave well-contoured areas untouched while smoothing areas of less than 5-2.5% slope (to lessen streaking in flat areas typical of multiple-profile DEM derivation). - cubic smoothing of elevation profile across contours to 35% of the distance between adjacent contours. This profiles have a smaller, but still discontinuous change in slope at contour intersection than if not rounded. - 9 cell diameter for smoothing reach, - use all 8 directions (from grid point to N, S, E, W ,NE, NW, SE, SW) for each cell, - no line feeds. export dem <contour data name> 2 10.00 10.00 2 1 4 80 2 0.35 9 8 0

10 mt gridding cell spacing is the maximun that can be meaningfully extracted from hypsography contour lines. This allows very good hypsographic contour reproduction in all areas except very flat ones. Elevation_resolution_ is 1 decimeter (0.1 meter). Elevation accuracy is 24,000 contour data, i.e. plus/minus half the contour interval.
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.
DEM visially inspected using Delta3D version 2.0, 1995 by John Dabritz and S. Phan of Infotec Development Inc. Checked for completness and drainage characteristics matching the USGS Hydrography Digital Line Graphs published at the same time as the model. Further validation for logical consistency performed previous to submission for archiving.
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 with equal to or less than intended horizontal RMSE error of the DEM. The testing of horizontal accuracy of the source materials is accomplished 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.
Horizontal_Positional_Accuracy_Value: 3 meters (estimated)
Digital elevation models meet horizontal National Map Accuracy Standards(NMAS) accuracy requirements.
A vertical RMSE of one-half of the contour interval of the source map is the maximum permitted. Systematic errors may not exceed the contour interval of the source graphic. Level 2 DEMs have been processed or smoothed for consistency and edited to remove identifiable systematic errors.
Vertical_Positional_Accuracy_Value: 6 to 8 meters
DEMs meet vertical National Map Accuracy Standards (NMAS) accuracy requirements. Vertical Positional Accuracy Vaue varies with each quad.
Originator: U.S. Geological Survey
Publication_Date: Unknown
Publication_Time: Unknown
Title: Albany
Publication_Place: EROS Data Center, SD
Publisher: U.S. Geological Survey
Type_of_Source_Media: mylar separate from original color separation plate
Calendar_Date: Unknown
Source_Currentness_Reference: Ground Condition
Source_Citation_Abbreviation: CONTOUR1
Source_Contribution: elevation values for interpolation
Originator: U.S. Geological Survey or National Geodetic Survey (NGS)(ed.)
Publication_Date: Unknown
Publication_Time: Unknown
Title: project control
Publication_Place: EROS Data Center, SD
Publisher: U.S. Geological Survey
Type_of_Source_Media: field notes
Calendar_Date: Unknown
Source_Currentness_Reference: Ground Condition
Source_Citation_Abbreviation: CONTROL1
Source_Contribution: ground control points
Originator: U.S. Geological Survey(ed.)
Publication_Date: Unknown
Publication_Time: Unknown
Title: photo ID number
Publication_Place: EROS Data Center, SD
Publisher: U.S. Geological Survey
Type_of_Source_Media: transparency
Calendar_Date: Unknown
Source_Currentness_Reference: Ground Condition
Source_Citation_Abbreviation: PHOTO1
Source_Contribution: elevation values from photogrametry
The process can be seen as divided into several tasks, each with associated sub-processes. A. Original Data Source Preparation 1. The United States Geological Service (USGS) office of Map Production (Mid Continent Mapping Center, Rolla, MO) selects the most recent original printing plates (1:24,000 or 1:25,000 scale) for each published quadrangle map. These plates are archived under controlled environmental conditions and are produced from the original map scripting materials onto dimensionally stable material (MylarŪ). A copy of the separate is made by contact methods onto photosensitive, opaque, dimensionally stable material. The separate plate copy is shipped to the USGS Mapping Applications Center (Reston, VA). B. The MAC scans the separate plate with an Ektaprint (a.k.a. Optronics) drum scanner with an aperture of 24um (corresponding to a linear resolution of approx 1030 DPI) into a run-length encoded (RLE) formatted raster file. Contours lines have typically a thickness of 25 to 30 pixels. The file, typically between 10 and 20 Mb, would be checked for completeness and distortion. If satisfactory MAC forwards both the raster file, the plate separate and the corresponding published quadrangle to the digitization workshop at the New York State Department of Environmental Conservation Water GIS unit in Albany, NY. B. Raster file batch processing 1. The raster file was loaded into Line Tracer for X Windows (LT4X, Infotec Inc., Portland, Oregon) version 3.1. With it is georegistered and trimmed of any excess margin. 2. The file is put through an automated raster-to-vector batch process in which a vector following the center of the raster line is created, with a minimum vertex separation of 25 pixels. Once the vector has been calculated and the topology of the resultant data established, the resolution of the original raster was reduced to 500 DPI, to allow faster processing in the succeeding steps. C. Vector Contour Edit, Edge Matching and Labeling. 1. The vectorized contours are edited carefully to correct any line breaks, vector webbing (due to pen thickness or lack of resolution of the original's drafting process), labels and special line symbols (depressions, road fills, etc). 2. The contours are labeled with their corresponding elevations, as tagged in the original material. 3. The eight adjoining maps's vector contours are brought in and checked against those of the map being edited. Vectors of matching labels are snapped together if the gap is less than 3 line-thicknesses. Otherwise they are tagged as *disagreement in the original' (see DLG standards for hypsography layer). For each border only one of the maps is edited. 4. An independent quality control check of contour edits and labeling is carried out. 5. The Digital Elevation Model is interpolated in a batch process (see "Native Dataset Environment" above). D. DEM Edit and Quality Control 1. The resultant DEM is loaded in Delta3D (Infotec Inc., Portland, OR) v. 2.1, together with the corresponding hydrography vectors. The DEM is - Irregular patterns - Water Body height and drainage along vector streams. Water retention areas (wetlands, marshes...) are not modified except for stream entrance and exit. - Edge matching with the adjoining eight DEMs. 2. From thirty to thirty-five height reference markers are collected from the corresponding cultural separate for the quadrangle. These are compared to heights as read from the DEM and an statistical RMS is calculated, this is recorded in the DEM's C record. 3. The quadrangle record A is filled and checked for consistency. 4. A final DEM-formatted elevation dataset for the quadrangle is recorded. E. Final Quality Control and Databasing 1. The DEM file is shipped to USGS's Rocky Mountain Mapping Center (Boulder, CO). There it undergoes a separate quality control process which essentially mimics D. 2. The corresponding quality control flags are established. The DEM is sub-sampled to 30 mt grid spacing and the resultant file is forwarded to USGS's EROS Data Center, were it is catalogued into the National Elevation database. The 10 mt grid spacing file is returned to NYS DEC, from where it is forwarded to Cornell University's Mann Library.
Process_Date: Unknown

Grid_Coordinate_System_Name: Universal Transverse Mercator
UTM_Zone_Number: 17 or 18 or 19
Scale_Factor_at_Central_Meridian: .9996
Longitude_of_Central_Meridian: +075.000000
Latitude_of_Projection_Origin: +00.000000
False_Easting: 0
False_Northing: 0
Planar_Coordinate_Encoding_Method: row and column
Abscissa_Resolution: 10
Ordinate_Resolution: 10
Planar_Distance_Units: Meters
Horizontal_Datum_Name: North American Datum of 1927
Ellipsoid_Name: Clarke 1866
Semi-major_Axis: 6378206.4
Denominator_of_Flattening_Ratio: 294.9787
Altitude_Datum_Name: National Geodetic Vertical Datum of 1929
Altitude_Resolution: 1
Altitude_Distance_Units: decimeters
Explicit elevation coordinate included with horizontal coordinates

The digital elevation model is composed of an elevation value linked to a grid cell location representing a gridded form of a topographic map hypsography overlay. Each grid cell entity contains an 8-character value between -32,767.0 and 32,768.0.
U.S. department of the Interior, U.S. Geological Survey, 1992, Standards for digital elevation models: Reston, VA, a hypertext version of the Digital Elevation Models - Data users Guide 5 is available at: <>

Contact_Organization: Albert R. Mann Library
Address_Type: mailing and physical address
Address: Cornell University
City: Ithaca
State_or_Province: New York
Postal_Code: 14853
Contact_Voice_Telephone: 607-255-5406
Resource_Description: 7.5-minute digital elevation models; 7.5-minute DEM
Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that careful attention be paid to the contents of the metadata file associated with these data. Neither the U.S. Geologial Survey nor the New York State Department of Environmental Conservation shall be held liable for improper or incorrect use of the data described and/or contained herein.

Metadata_Date: 19980805
Metadata_Review_Date: 19990323
Contact_Person: Barbara Cruden
Contact_Organization: New York State Department of Environmental Conservation
Address_Type: mailing and physical address
Address: 50 Wolf Rd.
City: Albany
State_or_Province: New York
Postal_Code: 12233
Contact_Voice_Telephone: 518-457-1307
Contact_Facsimile_Telephone: 518-457-0738
Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata
Metadata_Standard_Version: June 1998

Generated by mp on Mon Nov 09 10:27:23 1998