Obtaining Gridded Data

Digital grids of the Puget Sound aeromagnetic survey can be downloaded from the directory, grids. Grids are available for the entire aeromagnetic survey and for each 1:100000-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 longitude), then using a minimum-curvature algorithm to interpolate values to rectangular grid intersections. Grid intersections are spaced 200 m apart.

All files are in Geosoft Grid Exchange Format (GXF), a standard ASCII format for exchanging gridded data among different software systems. Software that supports the GXF standard will be able to properly import formatted GXF files. GXF is described more fully in this "readme" file and this "gxf.pdf" Acrobat Reader file

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. It too is described more fully in the "readme" file.

The following aeromagnetic grids are available:

1:100,000-scale quadrangle maps

• Bellingham (bellingham.gxf.gz (462 KB))
• Centralia (centralia.gxf.gz (132 KB))
• Mount Olympus (mount_olympus.gxf.gz (248 KB))
• Mt. Baker (baker.gxf.gz (231 KB))
• Port Angeles (port_angeles.gxf.gz (149 KB))
• Port Townsend (port_townsend.gxf.gz (446 KB))
• Roche Harbor (roche_harbor.gxf.gz (132 KB))
• Sauk River (sauk_river.gxf.gz (198 KB))
• Seattle (seattle.gxf.gz (462 KB))
• Shelton (shelton.gxf.gz (264 KB))
• Skykomish River (skykomish_river.gxf.gz (182 KB))
• Snoqualmie Pass (snoqualmie_pass.gxf.gz (231 KB))
• Tacoma (tacoma.gxf.gz (479 KB))

1:500,000-scale map

• Entire survey (all.gxf.gz (3.3 MB))