The Road Indicator Project (TRIP) NORM ED Datasets
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The National Overview Road Metric Euclidean Distance (NORM ED) dataset was developed to describe the extent and configuration of the spaces between roads in the United States. The metric of NORM ED is Euclidean distance, in units of meters, to the nearest road. The NORM ED value at any point estimates the largest radius of a circle, centered at that point, that contains no roads. Accuracy of the estimate is limited by the accuracy of the source data, both in terms of roads depicted and their positions. NORM ED considers all roads to be equal, regardless of road surface, width, and traffic volume. The dataset from which NORM ED was built contains features ranging from interstate highways to jeep tracks, although not necessarily with uniform detail or reliability in all areas. The full-resolution dataset provides distance-to-road (DTR) values on a 30-meter image, using an equal-area projection. NORM ED values can be aggregated statistically-by averaging, for example-over areas of the user's choice, and results are mathematically valid. NORM ED can therefore be used to calculate comparable average DTR values for counties, states, watersheds, ecoregions, or any other area of interest. Name Last modified Size Description Data Disclaimer TIGER 2000 and Dynamap 1000 do not contain data that describes their revision status either by individual feature or by area. Thus, the source data for NORM ED represent conditions over a range of collection and compilation dates and are not a true temporal snapshot of road conditions of the United States. Nevertheless, this is the most complete current dataset intended to portray all roads across the nation. It fairly represents the overall status of documented roads in the U.S. approximately for the year 1999, although detailed comparison of Dynamap 1000 data with 1990's aerial photographic images reveals discrepancies, usually in the form of roads missing from Dynamap 1000, in many areas. We have not made comparisons in enough places to make quantitative statements about error rates or magnitudes. We note, however, that comparison of DTR values between various data sources is an effective method of comparison; small shifts in vector road positions have modest effect, whereas addition or subtraction of roads causes substantial DTR change. Because of the discrepancies in revision status of these maps, they would not be valid data for use in an Environmental Impact Statement. Department of Interior Disclaimer Information presented on this website is considered public information and may be distributed or copied. Use of appropriate byline/photo/image credit is requested. We strongly recommend that USDOI data be acquired directly from a USDOI server and not through other sources that may change the data in some way. While USDOI makes every effort to provide accurate and complete information, various data such as names, telephone numbers, etc. may change prior to updating. USDOI provides no warranty, expressed or implied, as to the accuracy, reliability or completeness of furnished data. Some of the documents on this server may contain live references (or pointers) to information created and maintained by other organizations. Please note that USDOI does not control and cannot guarantee the relevance, timeliness, or accuracy of these outside materials. |
U.S. Department of the Interior |
U.S. Geological Survey
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Page Last Modified: Wednesday, 14-Nov-2007 18:29:03 Mountain Standard Time
