J. Pach and P. K. Agarwal, Combinatorial geometry. Wiley-Interscience Series in Discrete Mathematics and Optimization, 1995.
DOI : 10.1002/9781118033203
URL : http://dx.doi.org/10.1016/0898-1221(96)87331-7

M. D. Penrose and C. A. Rogers, Random Geometric Graphs Packing and covering, Cambridge Tracts in Mathematics and Mathematical Physics, issue.54, 1964.