Our distances are not driving distances, but are calculated as a 'straight-line' (or point-to-point) distance from Lorton. A straight line distance ignores things like rivers, canyons, lakes, et cetera - it's truly a line drawn from Point A (ie- Lorton) to Point B.
Our distance measurements begin at a specific point in Lorton. The point that we are using is located at these GPS coordinates - Latitude: 33.7554, Longitude: -87.0622 [Map]. In this case, the coordinates for Lorton have been provided by the Geographic Names Information System (GNIS).