Heh. I can't explain everything in a forum post (I do teach a college class on the subject though). Basically, these show the Shadowrun country borders (I've now finished the entire planet minus every Trans-Polar Aleut island) at a very fine detail (c. 50m accuracy) using existing administrative borders and natural features where the Sixth World Atlas map diverged from the real world. If you can use shapefiles this is (AFAIK) by FAR the most accurate Shadowrun map ever created,
and it serves as a base that can then be attached to other data (like population numbers) to allow better visualization of information that is scattered around various sourcebooks. It can also be extended to map the internal political divisions when such information is available.
Want to overlay rail lines to see if they passed through the Gold and Ivory Coast area you are running in? Want to overlay climate data over the Shadowrun map? Need to see EXACTLY where the Sioux/UCAS border meets? If so, this can help. I've also created a KMZ version of the file that may be of use for those using software that doesn't read shapefiles.