Originally Posted by borked

Surrounding areas are calculated from latitude/longitude parameters of the visitor IP - complicated maths cos the world isn't flat ;)
$theta = $lon1 - $lon2;
$dist = sin(deg2rad($lat1)) * sin(deg2rad($lat2)) + cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * cos(deg2rad($theta));
$dist = acos($dist);
$dist = rad2deg($dist);
$miles = $dist * 60 * 1.1515;
$unit = strtoupper($unit);

Surrounding areas can be turned off in that add image:

Nearby ON: and with Nearby OFF: