We're a wireless ISP in north alabama. We've given Brian the GPS coords of our towers and he has drawn a circle around them at a 10 mile radius. He has also taken the zip code of all WISPs who have registered with him and done the same. A few WISPS have actually been able to give him exact coverage data and if he has that, he's placed that on the map (look in northeast alabama for example). Overall, it is a good representation of where there is a WISP presence - even if you may not have heard of us.
The ZIP code of their mailing/office address? That seems like a pretty silly approach.
Some of the WISPs around here in the past were real fly-by-night operations, and the "office" was the basement of the guy's house -- nowhere near his towers.
·