Most of this data doesn't affect us. Amassing information alone doesn't mean it's valuable. Yet the new ability to mine the right information, discover patterns and relationships, already affects our everyday lives.
Anyone, for instance, who has a navigation screen on a car dashboard uses data streaming from 24 satellites 11,000 miles above Earth to pinpoint his or her exact location. People living in Los Angeles and dozens of other cities now participate, knowingly or not, in the growing phenomenon of "predictive policing" – authorities' use of algorithms to identify crime trends. Tennis fans use IBM SlamTracker, an online analytic tool, to find out exactly how many return of serves Andy Murray needed to win Wimbledon.
When we use sites like SlamTracker, companies take note of our browsing habits and, through either the miracle or the meddling of Big Data, use that information to send us personal pitches. That's what happens when AOL greets you with a pop-up ad (Slazenger tennis balls – 70 percent off!).
In their book, "Big Data: A Revolution That Will Transform How We Live, Work, and Think," Kenneth Cukier and Viktor Mayer-Schönberger mention Wal-Mart's discovery, gleaned by mining sales data, that people preparing for a hurricane bought lots of Pop-Tarts. Now, when a storm is on the way, Wal-Mart puts Pop-Tarts on the shelves next to the flashlights.
But what excites and concerns people about Big Data is more far-reaching than that. One way of seeing the bigger picture: taking a closer look at some of the people in the digital trenches.
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I follow Mandelbaum and Mr. Youkel down a corridor of the Library of Congress, past exhibits redolent of history and what you might expect from what we call "America's library," with its 38 million books on 838 miles of shelving.