“A vast body of research has shown [mobility] data is highly reidentifiable. Previously, researchers showed that knowing four random points of someone’s trajectory points, such as when and where you take your morning coffee, was enough to uniquely identify that person 95% of the time in a dataset of 1.5 million people. Other studies have replicated similarly high unicity numbers with location data obtained from vehicles, smart cards in public transport, credit card transactions and mobile phone metadata in a number of countries.”

” But what happens when the dataset is much bigger? Do trajectories get ‘lost in the crowd’ and become effectively anonymous?”

Per a study conducted by Ali Farzanehfar and Florimond Houssiau the answer is “No.”

“People remain unique in population-scale datasets, and thus that dataset size is not sufficient protection for individual privacy. The reidentification risk is still very high even for a population of 20 million people (93% of people unique with three points).”

Read details of their research via the International Association of Privacy Professionals.