How does a tunneling microscope collect data and construct an image?
The tunneling effect is highly non-linear with distance.  This is exploited by the microscope in that only the very tip of the needle gets any tunneling current.  In effect, the needle "looks", thru the "lens" of tunneling, to be greatly elongated and a lot sharper than it really is to the material under test.  Put another way, the tunneling effect makes a sharper and finer effective needle from a blunter physical one.

This needle is displaced small amounts electrically to maintain constant tunneling current as it moves over the sample.  The displacement can be made reasonably linear with the driving signal.  The driving signal then gives a profile of sample height as the needle scans the material.  The driving signals from multiple scans are put together to form a image.

This is certainly oversimplified, but that's the basic concept.  Surely there is much out there on scanning tunneling microsopes.