If you’re looking for an interesting read on some of the behind the scenes work on the Snowden leaks from a few years back, it’s hard to beat a book by one of the reporters who wrote it up.
It is, like most other reading on the subject, a depressing read that makes one wish to quit using the internet and modern technology entirely.
The core question of this book is, “If I observe information about your activities, pull it into a database, perhaps do some computation on it, but don’t actually see that result, have I collected anything on you?”
Unfortunately, I am familiar enough with some of the stuff discussed in the book to believe that it’s pretty much accurate.