New documents show how the NSA infers relationships based on mobile location data

Everyone who carries a cellphone generates a trail of electronic breadcrumbs that records everywhere they go. Those breadcrumbs reveal a wealth of information about who we are, where we live, who our friends are and much more. And the National Security Agency is collecting location information in bulk -- 5 billion records per day worldwide -- and using sophisticated algorithms to assist with US intelligence-gathering operations. How do they do it? And what can they learn from location data? The latest documents show the extent of the location-tracking program.