Here’s a great example. The New York City Taxi and Limousine Commission records and keeps data on every taxi fare, including the driver, vehicle, start and finish addresses and the fare and tip. Makes sense, and I am sure most western cities have something similar.
But because it is a public authority, then the data belongs to the public as long as it doesn’t breach the privacy of individuals. A freedom of information request caused this massive dataset to become available online.
The only personal information was the names of the drivers, and these were obscured in the data release (since unscrambled!). Unfortunately the government body didn’t appreciate how many taxi journeys begin or end at home. Or work. In some cases this information, on its own but more probably combined with other collaborating data, can actually show the journey a particular known individual took.
An example provided used photos of celebrities entering taxis to find the pick up point and time to search the database with.
Just because privacy laws are in place, doesn’t mean that you can trust the people in charge, and also of course people make errors of judgement.