How do owls do that?

[Jim Ferer]

No: HPFGUIDX 12200

Meredith:" We see several times (most specifically in GoF when Hedwig 
is finding Sirius) that when sending owl post, the owls can find 
people pretty much anywhere they are, right?  Why then in PoA did 
nobody ever send an owl to Sirius and just follow it on broomstick to 
find his whereabouts?"

Here's my offering:

Owls do things like fly hundreds, even thousands of miles, in a short 
time, so in many cases they aren't physically "flying" the way we 
understand it.  Of course, we have examples of brooms making 
ridiculously long journeys (Charlie's friends who carried Norbert to 
Roumania).

It's possible to make a location Unplottable so it can't be found on a 
map; Hermione mentions it in GoF.  It should therefore be possible to 
make something Unfollowable as well.