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OFR 99–0557: Readme File
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U.S. Geological Survey

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

Version 1.0  

By U.S. Geological Survey


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 U.S., 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


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.


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. logo