show/hide this revision's text 2 added ref

See

http://mathoverflow.net/questions/75030/clique-sizes-in-a-unit-disk-graph

and references mentioned there... Your graphs are the unit disk graphs of the title.

EDIT

See http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.7.4866&rep=rep1&type=pdf, especially the reference to Gupta/Kumar at the very beginning...

show/hide this revision's text 1

See

http://mathoverflow.net/questions/75030/clique-sizes-in-a-unit-disk-graph

and references mentioned there... Your graphs are the unit disk graphs of the title.