If you're using perl, you can do something like..
With an invisible man at the center point:
Code:
sub EVENT_SPAWN
{
$x = $npc->GetX();
$y = $npc->GetY();
$z = $npc->GetZ();
quest::set_proximity($x - 5, $x + 5, $y - 5, $y + 5, $z - 6, $z + 10);
}
sub EVENT_ENTER
{
#something happens
}