Harry Potter: How did Snape track Harry to give him the sword?

Is there canon on this? I was watching the movie and it really didn't explain. Death Eaters are searching right and left and can't find him, but Snape has no trouble?

I was wondering if it were canon but do have a couple of theories:

1. Most likely, the sword gave itself to Harry (moving itself into the lake) and Snape, whom we know had the sword, followed it.


2. Ron's deluminator came from Dumbledore. It's possible the process that returned Ron to Hermione (that green ball of light) was something Snape could track. Of course that would mean that Dumbledore would have had to tell Snape to keep an eye out for it.