The National Hydrography Dataset (NHD) is

a newly combined dataset that provides

hydrographic data for the United States. The

NHD is the culmination of recent cooperative

efforts of the U.S. Environmental Protection

Agency (USEPA) and the U.S. Geological

Survey (USGS). It combines elements of

USGS digital line graph (DLG) hydrography

files and the USEPA Reach File (RF3). The

NHD supersedes RF3 and DLG files by

incorporating them, not by replacing them.

Users of RF3 or DLG files will find the same

data in a new, more flexible format. They will

find that the NHD is familiar but greatly

expanded and refined.

The DLG files contribute a national coverage

of millions of features, including water bodies

such as lakes and ponds, linear water features

such as streams and rivers, and also point

features such as springs and wells. These files

provide standardized feature types, delineation, and spatial accuracy. From RF3, the

NHD acquires hydrographic sequencing,

upstream and downstream navigation for

modeling applications, and reach codes. The

reach codes provide a way to integrate data

from organizations at all levels by linking the

data to this nationally consistent hydrographic

network. The feature names are from the

Geographic Names Information System

(GNIS). 

The NHD provides comprehensive coverage

of hydrographic data for the United States.

Some of the anticipated end-user applications

of the NHD are multiuse hydrographic

modeling and water-quality studies of fish

habitats. Although based on 1:100,000-scale

data, the NHD is planned so that it can

incorporate and encourage the development

of the higher resolution data that many users

require. The NHD can be used to promote the

exchange of data between users at the

national, State, and local levels. Many users

will benefit from the NHD and will want to

contribute to the dataset as well.

Characteristics of the National

Hydrography Dataset

 It is a feature-based dataset that 

interconnects and uniquely identifies the 

stream segments or "reaches" that make 

up the Nation's surface water drainage 

system. 

 Unique reach codes (originally developed 

by the USEPA) are provided for networked features and isolated water bodies 

 The reach code structure is designed to 

accommodate higher resolution data. 

 Common identifiers uniquely identify 

every occurrence of a feature. 

 It is currently based on the content of the 

USGS 1:100,000-scale data, giving it 

accuracy consistent with those data. 

 Data are in decimal degrees on the North 

American Datum of 1983. 

 Names with GNIS identification numbers 

are included for lakes, other water bodies, 

and many stream courses. 

 It provides flow direction and centerline 

representations through surface water 

bodies. 

Maintaining the NHD

The NHD is designed to accommodate both

the higher resolution data that many users

need and the 1:100,000 scale data. The higher

resolution data will be incorporated into the

NHD through the participation of users at the

national, State, and local levels. The common

identifiers for the features are the basis for

tracking and sharing deletions, additions, and

modifications of features during maintenance.

They are used to com-municate and share

corrections among organizations. The NHD

will improve the integration of hydrographically related data in support of the varied

applications of a growing national user

community, and it will also enable shared

maintenance and enhancement.

Obtaining Data from the NHD

The data are now available for downloading

by cataloging unit from the USGS at

nhd.usgs.gov. The cataloging unit is a

geographic area that subdivides the

accounting units within hydrologic units.

Most of the more than 2,100 cataloging units

for the Nation are larger than 700 square

miles (1,813 square kilometers).

The data are available in two formats:

ARC/INFO workspace and Spatial Data

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 106-99

May 1999

The National Hydrography Dataset

In the upper left, the irregular shapes on and around the shaded image of Kentucky are the hydrologic cataloging

units that are in the State of Kentucky. On the right is a closer high- level view of three cataloging units, showing

their hydrographic features and labeled with the names and numbers of the units. In the oval, a small area is

enlarged to show examples of individual features with their reach codes. Note that the reach codes incorporate

the eight-digit number of the cataloging unit in which they lie.
Transfer Standard. Each format is delivered

as tarred and compressed files. Data on

compact disc-readable is available for order

through the USGS Global Land Information

System. 

Information

More information about the NHD can be

found at nhd.usgs.gov.

For information on other USGS products and

services, call 1-888-ASK-USGS, or visit the

general interest publications Web site on

mapping, geography, and related topics at

erg.usgs.gov/isb/pubs/pubslists/.

For additional information, visit the

ask.usgs.gov Web site or the USGS home

page at www.usgs.gov.

Any use of trade, product, or firm names is

for descriptive purposes only and does not

imply endorsement by the U.S. Government.