U.S. DEPARTMENT OF THE INTERIOR

                          U.S. Geological Survey










 Digitized Aeromagnetic Datasets for the Conterminous United States, Hawaii,
                              and Puerto Rico

                                Version 1.0






                                    By




                          U.S. Geological Survey





                          Open-File-Report 99-557

README.TXT

About This CD-ROM

From 1976 through 1999 (and on a continuing basis), the U.S. Geological
Survey digitized analog magnetic maps for various regions of the United
States. The purpose of this program is to fill in gaps that are not covered
by modern digital aeromagnetic surveys.

This CD-ROM contains all available digitized magnetic files that are
currently on record at the U.S. Geological Survey for the continental US,
Hawaii and Puerto Rico. Updates will be made available to the public as
they are released on our FTP sites.

Data Format and Digitizing Technique for XYZ Files

Format:

Longitude, Latitude, Magnetic Field Value - (2f11.4, f8.1)

   * Longitude - decimal degrees
   * Latitude - decimal degrees
   * Magnetic Field Value - nanoTesla or gamma

NOTE: longitude and latitude are defined to four decimal places (10 meter
resolution) because this is the most reasonable accuracy that can be
standardized for the variety and scaling of the original maps.

*.JPG images of the data were created using a Geographic Coordinate
(longitude, latitude) System and the Clarke 1866 datum.

Technique:

The procedure used to digitize the XYZ files was one of the following three
methods:


  1. flight line/contour line crossing and interpolation of values along
     the flight lines.
  2. flight line/contour line crossing and inflection points of contour
     lines between flight lines.
  3. contour lines without regard to flight line positions.

How to Run This CD-ROM

   * Load the CD-ROM into the user’s CD-ROM reader and read the readme
     file. Change the directory to E:\html (E is assumed to be the users
     CD-ROM reader).

   * If you are running this CD on a PC using Windows 95, 98, 2000 or NT,
     or on a Macintosh, simply double click on the file named
     "mag_home.htm".

   * For UNIX and Windows 3.x systems, load your browser into memory and
     then execute the "mag_home.htm" file.

NOTE: This CD-ROM was developed on a Pentium II PC using the Hyper Text
Markup Language. It was tested extensively using NETSCAPE versions 3.0
through 4.65 and MS Internet Explorer versions 3.0 through 5.0. Testing of
the CD was done for Apple Macintosh and on a SUN UNIX System. In theory
because this is an HTML product, it should run on most platforms using
various browsers.

If you have any questions or problems about the data on this CD-ROM, please
contact Bob Kucks at 1-303-236-1405 or Pat Hill at 1-303-236-1343.

*This report is preliminary and has not been reviewed for conformity with
U.S. Geological Survey editorial Standards. Use of brand names is for
descriptive purposes and does not constitute endorsement by the U.S.
Geological Survey.