a graph puzzle

[Max Alekseyev]

Good morning,

I've generated a graph on the unordered co-prime pairs of non-negative
integers below 30,
using some quite "natural" mapping.

The graph has quite nice and somewhat fractal structure:
http://img505.imageshack.us/img505/4065/3cbv7.jpg  (its size is ~ 800KB)

Can you guess what is the underlying mapping "hidden" in this graph?

Regards,
Max

P.S. I hate puzzles like this one but maybe you like ;)

P.S. Actually, my concern is whether this mapping is present in OEIS
in either form.