The paper under discussion is a very well-written and interesting piece of work by Secchi et al. (2015) dealing with spatio-temporal data on mobile phone use in the area of Milan. I congratulate the authors for such a stimulating and interesting paper. It clearly points out that Erlang data on mobile phone use contain a large amount of rich information. The paper is an excellent example of statistical analysis of Big Data. I discuss briefly two alternative ways of dimension reduction of spatio-temporal data and illustrate them with artificial data that has been simulated according to the scheme proposed by the authors.

Peer Reviewed