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.
Hypsography Attribute Coding is found at http://www.fws.gov/data/gisconv/hp.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.

Hypsography data is contour information. It should match well with Digital Elevation Model (DEM) data for any given area. Generally, this data layer will be used in conjunction with other data layers such as soils (for slope analysis), possibly wetland information for pond sites, etc. The usefulness of the data will likely depend on the intervals between the contours, and the detail needed for analysis.

Some software programs are capable of generating hypsography data from DEM data. If you have newer DEM data in an acceptable scale, this may be a good alternative, as some of the hypsography data is quite old. In areas where there has been little development or other geographic change, however, the date of the data may be irrelevant.

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.

The fields are labeled major1, minor1, and description in the Dbase file. There are actually more fields than this in the DLG file; major1, minor1, major2, minor2, major3, minor3, and description in the ones checked. The dbf file can be used as a lookup for any of the major/minor combinations, as the codes are the same in each case. In the sample files checked, the major1/minor1 fields indicated that the line was a contour, and the major2/minor2 field (with few exceptions) indicated the elevation in meters.

Also included is a readme.hp file, with specific notes on the other two files. Although these files were originally created for the 1:100,000-scale data, the attribute information has been edited so that it should work for all scales of data in DLG format.

Tools for using the data in SDTS format will be referenced here when available.

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