The research uses community detection methods from network science to partition the callers in a data set of 6 billion phone calls, allowing them to detect spatial boundaries produced by social interactions. Callers in each ‘community’ contain stronger internal communication ties to other members of the same community than they do to those outside of it.
Sometimes these regions match political and topographic boundaries closely, but in other cases new regional boundaries are detected, as is the case here with Wales and the West Country, which form a single contiguous region. A region West of London is also detected, a belt of high-tech activity including Buckinghamshire and Oxford, which seems to form a single community.
You can read the open-access paper at PLOS.