A favorite pastime of Internet users is to share their location: services like Google Latitude can inform friends when you are nearby; another, Foursquare, has turned reporting these updates into a game.
But as a German Green party politician, Malte Spitz, recently learned, we are already continually being tracked whether we volunteer to be or not. Cellphone companies do not typically divulge how much information they collect, so Mr. Spitz went to court to find out exactly what his cellphone company, Deutsche Telekom, knew about his whereabouts.
The results were astounding. In a six-month period — from Aug 31, 2009, to Feb. 28, 2010, Deutsche Telekom had recorded and saved his longitude and latitude coordinates more than 35,000 times. It traced him from a train on the way to Erlangen at the start through to that last night, when he was home in Berlin.
Mr. Spitz has provided a rare glimpse — an unprecedented one, privacy experts say — of what is being collected as we walk around with our phones. Unlike many online services and Web sites that must send “cookies” to a user’s computer to try to link its traffic to a specific person, cellphone companies simply have to sit back and hit “record.”
“We are all walking around with little tags, and our tag has a phone number associated with it, who we called and what we do with the phone,” said Sarah E. Williams, an expert on graphic information at Columbia University’s architecture school. “We don’t even know we are giving up that data.”
Tracking a customer’s whereabouts is part and parcel of what phone companies do for a living. Every seven seconds or so, the phone company of someone with a working cellphone is determining the nearest tower, so as to most efficiently route calls. And for billing reasons, they track where the call is coming from and how long it has lasted.
“At any given instant, a cell company has to know where you are; it is constantly registering with the tower with the strongest signal,” said Matthew Blaze, a professor of computer and information science at the University of Pennsylvania who has testified before Congress on the issue.
Mr. Spitz’s information, Mr. Blaze pointed out, was not based on those frequent updates, but on how often Mr. Spitz checked his e-mail.
Mr. Spitz, a privacy advocate, decided to be extremely open with his personal information. Late last month, he released all the location information in a publicly accessible Google Document, and worked with a prominent German newspaper, Die Zeit, to map those coordinates over time.
“This is really the most compelling visualization in a public forum I have ever seen,” said Mr. Blaze, adding that it “shows how strong a picture even a fairly low-resolution location can give.”
In an interview from Berlin, Mr. Spitz explained his reasons: “It was an important point to show this is not some kind of a game. I thought about it, if it is a good idea to publish all the data — I also could say, O.K., I will only publish it for five, 10 days maybe. But then I said no, I really want to publish the whole six months.”
In the United States, telecommunication companies do not have to report precisely what material they collect, said Kevin Bankston, a lawyer at the Electronic Frontier Foundation, who specializes in privacy. He added that based on court cases he could say that “they store more of it and it is becoming more precise.”