How is the distance to other members and posts calculated?
When viewing messages, the distance is from your account location* to the approximate location of the other member. The distance is only an estimate.
When viewing posts, the distance is from your account location* to the location that the post was mapped to. Most posts are not mapped to the exact location where the person or item is so the distance is only an estimate. To view the location a post was mapped to, look at the map that is shown further down on the post view page.
All distances are "as the bird flies" (straight lines between the points) so actual travel distance will usually be greater.
*To view or change your account location, use the Post Options on the Settings page.