There are a couple of ways I have come across - one is specifically for families and is like a family tree. I did one with us in the middle and just lines out to different individuals, with thicker lines for the strongest relationships and directly from one or the other for individual rather than joint friends. I've just drawn somehting in "paint", but can't add it here?
I don't know of anything specific online but a search on eco maps may throw up something.
Bop