README.TXT FILE FOR GRIDDED DATA TRANSFER 

This FTP directory contains digital grids computed from the 
Puget Sound aeromagnetic survey.  Grids are available for 
the entire survey and for each 1:100,000-scale quadrangle 
covered by the survey. All grids were computed by 
transforming flight-line point data to Lambert Conformal 
Conic projection (central meridian 122 degrees west), then 
using a minimum-curvature algorithm to interpolate values to 
rectangular grid intersections. Grid intersections are 
spaced 200 m apart.

All grids are in Geosoft Grid eXchange Format (GXF), a 
standard ascii format for exchanging gridded data among 
different software systems. GXF has been adopted by the 
Society of Exploration Geophysicists (SEG), the Canadian 
Exploration Geophysical Society (KEGS), and the Australian 
Society of Exploration Geophysicists (ASEG) as the standard 
format for exchanging gridded gravity and magnetic data.  
Software that supports the GXF standard (e.g., Arc/Info and 
OASIS/Montaj) will be able to properly import these 
formatted GXF files.  A complete description of GXF is 
provided in the document gxf.pdf provided by Geosoft, Inc., 
and located in this FTP directory.  Additional information 
is available at http://www.geosoft.com.

To speed file transfers, all files have additionally been 
compressed into the public-domain "gzip" format (as 
indicated by the suffix .gx). Gzip format is commonly used 
on PC DOS, PC Windows, Macintosh, and Unix platforms. 
Information on gzip is available at:

 http://www.maths.lancs.ac.uk/~smithdm1/GNU/GNUWeb/gzip.html 
   (unix and PC DOS versions)

 http://www.winzip.com/ 
   (PC windows version)

 http://www.1source.com/tools/compress.html
   (contains link to download Mac gzip)

The following aeromagnetic grids are available in this 
directory:

      Bellingham (bellingham.gxf.gz)
      Centralia (centralia.gxf.gz)
      Mount Olympus (mount_olympus.gxf.gz)
      Mt. Baker (baker.gxf.gz)
      Port Angeles (port_angeles.gxf.gz)
      Port Townsend (port_townsend.gxf.gz)
      Roche Harbor (roche_harbor.gxf.gz)
      Sauk River (sauk_river.gxf.gz)
      Seattle (seattle.gxf.gz)
      Shelton (shelton.gxf.gz)
      Skykomish River (skykomish_river.gxf.gz)
      Snoqualmie Pass (snoqualmie_pass.gxf.gz)
      Tacoma (tacoma.gxf.gz)
      Entire survey (all.gxf.gz)