U.S. Fish & Wildlife Service

Data Layer: HYDROGRAPHY (DLG)

You are invited to read the definitions of terms used in this data standard.

Name Hydrography (DLG)
Description
 The data consists of digital information input by the U.S. Geological Survey (USGS) depicting streams, rivers, and related types of features. Although these data now exist in Spatial Data Transfer Standard (SDTS), as well as Digital Line Graph (DLG) format, they are still called DLG data. The data are available on the Internet, free-of-charge, or on inexpensive CD's. The CD's contain 1:100,000- and 1:2,000,000-scale data in DLG format, available nationally. The 1:24,000-scale data on the Internet  is available only in SDTS format. While it is not yet completed nationally, work is in progress.
Source
 USGS EROS Data Center at http://edc.usgs.gov/geodata/ is the source for 1:100,000-scale data in DLG format.
SDTS information is at http://mcmcweb.er.usgs.gov/sdts/data.html for USGS data available in SDTS format.
Reference(s)

Part 270, FW 6, Data Management and Standards, dated September 30, 2002.

USGS DLG Data is found at http://edc.usgs.gov/products/map/dlg.html. This site includes a section on SDTS data, as well as DLG optional data.
The Data User's Guide is available from http://geography.usgs.gov/standards/. Complete DLG documentation, selectable by scale at the site; very large documents.
Hydrography Attribute Coding is found at http://www.fws.gov/data/gisconv/hy.zip. This updated document on the attribute codes gives a detailed definition of each code and describes how they were created. It is in WordPerfect 5.1 format, zipped with PKZip. A complete set of this updated documentation for DLG data is also available at the Data User's Guide site referenced above, in the dlgstnds subdirectory.
The SDTS Information Site is at http://mcmcweb.er.usgs.gov/sdts/. This site includes documentation, FAQ's, and data pointers.

Use Instructions
 The USGS Hydrography data layer in DLG format should be used wherever it is available in an appropriate scale and with current information. Other supplementary data may be needed if the USGS data is old or not in the large-scale format. In many parts of the country, TIGER data at the 1:24:000- scale may be a good alternative. The attribute data in the Tools section below will increase the usefulness of the DLG attribute data by making it easier to associate more information with the base DLG file.

Hydrography data is often used as a reference GIS layer, but may be used in analysis as well. Future plans for this data set by USGS include upgrading the data set to include all the River Reach information supplied by the U.S. Environmental Protection Agency. Links to existing data will be established, so it is important to use the standard Hydrography data whenever possible, in order to take advantage of the planned increases in data functionality. Tools for utilizing the current DLG format data are listed below.

Limitations: Data should always be used at the scale appropriate to the application. The USGS makes every effort to achieve a high level of accuracy in all of its published products. An important aim of its accuracy control program is to meet the U.S. National Map Accuracy Standards. These standards vary with scale; for example, 1:24,000-scale data will be much more spatially accurate than data at the 1:100,000-scale. If the degree of precision is very important to the application, check the above reference to make sure the data being used are appropriate.

Tools
Hydrography attribute data can be found at http://www.fws.gov/data/gisconv/dlghydro.zip. These are files containing a list of the attribute codes in Dbase III file (dbf) and WordPerfect 5.1 (textual) format, zipped with PKZip. The codes have the same descriptions in both files when they are present in both files. The dbf file contains only codes currently in use. The WordPerfect document also contains older or deleted codes displayed in italics within parentheses.

The columns in the Dbase file are Major1, Minor1, Description, and Sdtsdlg, providing links to columns in the actual DLG data. Also included is a readme.hy file, with specific notes on the other two files.

SDTS Data Conversion Overview - There are some tools now available to convert Hydrography data in the SDTS format into other formats. Some of the tools work for the line, as well as the polygon, coverage; others only work on the line data. The SDTS tools are undergoing further development, and new tools will be posted when they are ready.

Visit the Documentation and Tools for Utilizing USGS DLG Data site for notes on all DLG data.

Phase Adopted
Approval Date January 14, 1999
Validation Date January 3, 2005
Data Steward Deb Southworth Green, National FWS GIS Coordinator, Branch of Data and System Services, Division of Information Technology Management

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These pages are maintained by the U.S. Fish and Wildlife Service, Division of Information Technology Management. Please feel free to contact Deb Southworth Green with any questions and comments.

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