The National Elevation Dataset (NED) is

a new raster product assembled by the

U.S. Geological Survey (USGS). The

NED is designed to provide national

elevation data in a seamless form with a

consistent datum, elevation unit, and

projection. Data corrections were made

in the NED assembly process to

minimize artifacts, permit edge

matching, and fill sliver areas of missing

data.

Data Characteristics

The NED has a resolution of 1 arcsecond (approximately 30 meters) for the

conterminous United States, Hawaii, and

Puerto Rico and a resolution of 2 arcseconds for Alaska. National Elevation

Dataset data sources have a variety of

elevation units, horizontal datums, and

map projections. In the NED assembly

process, the elevation values are

converted to decimal meters as a

consistent unit of measure, North

American Datum 1983 is consistently

used as horizontal datum, and all the data

are recast in a geographic projection.

Older digital elevation models (DEM)

produced by methods that are now

obsolete have been filtered during the

NED assembly process to minimize

artifacts that are commonly found in data

produced by these methods. Artifact

removal greatly improves the quality of

the slope, shaded-relief, and synthetic

drainage information that can be derived

from the elevation data. Figure 2

illustrates the results of this artifact

removal filtering. NED processing also

includes steps to adjust values where

adjacent DEM’s do not match well and

to fill areas of missing data between

DEM’s. These processing steps ensure

that the NED has no void areas and

artificial discontinuities have been

minimized. 

As higher resolution or higher quality

data become available, the NED is

updated to incorporate the best available

coverage. As the USGS's 7.5-minute and

15-minute digital elevation products near

completion for the conterminous United

States and Alaska respectively, NED data

will soon incorporate these sources. For

the small areas that are not yet covered,

the lower resolution 30-minute and 1-

degree USGS DEM products were

interpolated to obtain values used in

NED. These original elevation files are

currently available at

http://edcwww.cr.usgs.gov/doc/edchome/

ndcdb/ndcdb.html. In cases where 7.5-

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 148-99

September 1999

National Elevation Dataset

Figure 1: A shaded-relief representation of the conterminous United States portion of the National Elevation Dataset (NED).

Elevation is portrayed as a range of colors, from dark green for low elevations to white for high elevations.

Figure 2: A shaded-relief representation of the Rockypoint, Wyoming, 7.5-minute digital elevation model is shown above on

the left. The same area is shown on the right after NED artifact filtering has been performed. The superimposed red lines

are synthetic drainage networks derived from each elevation dataset.
minute DEM’s have 10-meter resolution,

the original source data will be at a

higher resolution than the NED. As

more data become available at a finer

resolution than that of the NED, the

feasibility of developing a finer

resolution NED will be investigated.

Metadata

The Federal Geographic Data

Committee's content standard for digital

geospatial metadata http://www.fgdc.gov/

metadata/contstan.html) will be used to

document NED data. Metadata about the

individual source datasets used to

assemble NED are presented in a

spatially referenced form. The polygonal

footprint of each part used from a source

dataset is retained during NED assembly

to provide the spatial context. The

attributes of each source dataset, such as

original resolution, production method,

and date entered into NED, are linked to

this polygonal footprint. All of these

source polygons together form a national

coverage. Through this spatially

referenced metadata, the information is

made available to the user regarding the

source data for any area of NED. For

example, a NED user might use the

spatially referenced metadata to identify

the parts of a study area that were

produced by obsolete production

methods. 

Applications

Elevation data are an essential part of

many earth science applications. They

are used for such diverse purposes as

providing shaded-relief backgrounds,

establishing stratification in land cover

classification, doing geometric and

radiometric correction of remotely

sensed data, indicating landform

characteristics such as slope and aspect,

and analyzing synthetic drainage

networks and watershed delineations

through the use of geographic

information systems. 

Obtaining Data

Plans are to have NED publicly available

by late 2000. The NED will be delivered

in the Spatial Data Transfer Standard

(SDTS) raster profile. The spatially

referenced metadata will be delivered in

SDTS topological vector profile. Other

formats may also be supported. An

Internet browse of NED shaded-relief

imagery with vector reference

information will be provided as an aid to

ordering. A customer can identify the

requested area graphically through the

Internet browser. That area of interest

will be extracted from the NED and from

the spatially referenced metadata and

formatted for delivery. The data will be

available to download from the Internet

using file transfer protocol or on standard

distribution media. As more information

on the NED becomes available, it will be

accessible through the Internet at

http://gisdata.usgs.gov/ned.

For more information, please contact:

Customer Services

U.S. Geological Survey

EROS Data Center

47914 252nd Street

Sioux Falls, South Dakota 57198-0001

Tel: 800-252-4547

Tel: 605-594-6151

Fax: 605-594-6589

Email: custserv@edcmail.cr.usgs.gov

Information

For information on these and other

USGS products and services, call 1-888-

ASK-USGS, use the Ask.USGS fax

service, which is available 24 hours a

day at 703-648-4888, or visit the general

interest publications Web site on

mapping, geography, and related topics

at http://mapping.usgs.gov/www/

products/mappubs.html.

Please visit the USGS home page at

http://www.usgs.gov/.