Our distances are not driving distances, but are calculated as a 'straight-line' (or point-to-point) distance that starts in Prestwick. A straight line distance ignores things like rivers, canyons, lakes, et cetera - it's truly a line from Point A (ie- Prestwick) to Point B.
Our distance measurements begin at a specific point in Prestwick. The point that we are using is located at these GPS coordinates - Latitude: 31.4529, Longitude: -87.9661 [Map]. In this case, the coordinates for Prestwick have been provided by the Geographic Names Information System (GNIS).