A by-product of the DEM/DOQ development process is a set of files (one for each quad) that has the contour lines tagged with the elevation it represents. These are vector files. This set of coverages have some edge-matching completed and additional error detection and corrections have been applied. The contour intervals are the same as the 7½-quads they are derived from. Those are usually in feet and vary from 5-foot (generally along the Platte or other river valleys) to 20-foot (generally in the Sandhills) intervals with 10-foot contours being the most common throughout the State. There are a few quads in the northwest part of Nebraska that are mapped in meters and those have a contour interval of 5 meters.
The tagged vector contours data can be used as a digital layer in various studies.
The edges of of each vector has been clipped to match the quad boundaries.
ground condition
None, Acknowledgement of the Nebraska Department of Natural Resources would be appreciated in products derived from this data
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The data was color-coded to help confirm corect attributing of contour elevation onto the vectors. This is not a 100% accurate representation of the contours from the 7 1/2 minute quads. In areas where the contours are close together, tagged vectors will only approximate the actual contour lines. Also, in "tight" areas, not all lines will be represented nor will they necessarily be contiguous lines.
This data was taken from the USGS 7.5 minute quadrangles
Since this is a product derived from the production of DEM/DOQ process and are created coverages from MOSS or DLG format, the fidelity of the relationships encoded in the data structure are atuomatically verified using a USGS software program upon completion of the data production cycle.
This is part of the DEM production cycle and DEMs have been completed and 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. It can be assumed that thes supplementary products will also meet production quality control limits.
The horizontal accuracy is expresssed 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 that 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.
7.5 minute topograhic quadrangle maps were scanned and the elevation lines tagged. Maybe accurate to 25 meters.
This is a development product of the DEM production cycle so the description of the DEM development will describe the Vertical_Positional_Accuracy_Report. The vertical RMSE statistic is used to describe the vertical accuracy of a DEM, encompassing both random and systematic errors introduced during production or 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 points data and comparison of the DEM with the quadrangle hypsography are conducted by the quality control units with 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 indentified 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 form unknown accidental causes. DEM's are edited to correctly depict elevation surfaces that correspond to water bodies of specified size, 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 beeen processed or smoothed for consistency and edited to remove identifiabe systematic errors. Level-2 DEMs have better resolution than Level-1 DEMs. Level 1 DEM: A RMSE of 7-meters or less is the desired accuracy standard. A RMSE of 15-meters is the maximum permitted. A 7.5-minute DEM at this level has an absolut elevation error tolerance of 50 meters (approximately three times th 15-meter RMSE) for blunder errors for any grid node when compared to the true elevation. Any array of points in the DEM can not encompass more than 49 contiguous elevations in error by more than 21 meters (three times the 7-meter RMSE). Systematic errors that are within stated accuracy standards are tolerated.
7.5 minute topograhic quadrangle maps were scanned and the elevation lines tagged. Maybe accurate to 25 meters.
hypsographic vector information
Since this is part of the DEM production sycle, the description of that cycle is presented here as representative of the process of creating the tagged vector coverages. The production procedures, instrumentation, hardware and software used in the collection of 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 production of standard USGS DEM datasets. Level 1 DEM: Level 1 DEM's are acquired photgrammetrically by manual profiling or image correlation techniques form National Aerial Photography Program (NAPP) or equivalent source photographs. Level 1 30-minute DEM's may be derived or resampled from level 1 7.5-minute DEM's. 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. The Nebraska Natural Resources Commission developed Level-2 DEMs for the entire state of Nebraska. Level 3 DEM: Level 3 DEM's are created from DLG data that has been vertically integrated with all categories of hypsography, hydrography, ridge line, break line, drain files and all vertical and horizontal control networks. The production of level 3 DEMs requires a system of logic incorporated into the software interpolation algorithms that clearly differentiates and correctly interpolates between the various types of terrain, data densities and data distribution. 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 inces 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 datsets 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 representaions by correcting the alignment of ridges and drains, and overall topographic shaping within a approximately 15-30 row or column grid post zone on both edges. Quality control: DEMs 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 dissemination by the Nebraska Department of Natural Resources and archiving in the National Digital Cartographic Data Base (NDCDB) utilizing the Digital Elevation Model Verification System (DVS) software.
301 Centennial Mall South
P.O. Box 94676
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Metadata imported.
Metadata imported.
301 Centennial Mall South
P.O. Box 94676
http://dnr.ne.gov
None
This data is in single precision format.
Spatial and attribute information
You can either order by leaving a message over the web or call Nebraska Department of Natural Resources.
You can order by leaving a message over the web or call Nebraska Department of Natural Resources.
301 Centennial Mall South
P.O. Box 94676
http://dnr.ne.gov