Also,
have a line on. Acquire information about something or someone, come to know. For example,
Sue got a line on some possible tennis partners, or
The realtor has a line on a number of vacant apartments. Similarly,
give someone a line on means "provide information about," as in
The librarian gave me a line on the books I would need. This idiom uses
line in the sense of "a direct course." [c. 1900] Also see
get a fix on.