frequent locations

So, I recently enabled my frequent locations on my iphone5. I wanted to see how closely this is actually tracking my movements. After all the claims I've read, that have been made about the specificity and seemingly moment by moment tracking, I was surprised to find that the tracking had lots of holes in the data of where I had been spending time. A number of the places I go regularly on a nearly daily basis didn't show at all. So how does this work? And why the claims of total surveilance when it seems more spotty??

The ones that aren't showing up? The NSA has those.