“Data! Data! Data!” Sherlock Holmes cried impatiently. “I can’t make bricks without clay.”

The sleuth’s insatiable hunger for petabytes of data presaged that of the National Security Agency’s by a little less than seven decades. Like the NSA, Holmes took a pointillistic view of the truth. Find as many facts as possible, he held, view them from as many angles as possible, turn them inside out or set them aside until you collect more facts, and then, like pouring iron into a mold, cast your most durable image of reality. “It’s an old maxim of mine that once you have eliminated the impossible, whatever remains, however improbable, must be the truth,” as Holmes stated in Arthur Conan Doyle’s “The Adventure of the Beryl Coronet.”

The age of Snowden has made well-known NSA’s demanding data desires. So, too, have we gotten a glimpse of how the agency’s information foundry works, that place where mathematicians massage the metadata of phone records and Web traffic with powerful relational database software to strip away the impossible in pursuit of the “truth.” Whether you believe the collection and analysis of your personal data is trivial or intolerable, the age of Snowden has alerted us all to the coming of the information singularity, where near perfect portraits and detailed biographies of us all can be assembled if enough computer power is thrown at a big enough data set.

“Records that once would have revealed a few scattered tiles of information about a person now reveal an entire mosaic — a vibrant and constantly updating picture of a person’s life,” U.S. District Judge Richard Leon wrote in his Klayman v Obama (pdf) opinion earlier this week, ruling the NSA’s bulk collection of phone data likely unlawful.

Judge Leon picked his mosaic metaphor shrewdly, knowing that the NSA and other agencies that handle classified information, such as the CIA and FBI, are not principled foes of the mosaic metaphor. Far from it. When it suits their purposes — which is often — federal agencies rely on the regulatory power of “mosaic theory” to knock down freedom of information requests from the press and others for seemingly innocuous material. The Code of Federal Regulations states this power succinctly. Agencies can, in some instances, classify compilations of unclassified government information because taken together and analyzed, the end product can be used to pierce the veil of what has been classified. Likewise, the government frequently rejects FOIA requests because it fears that declassified information can be combined with public domain information to reveal classified information. “[T]he ‘mosaic’ approach,” the code states, is “the concept that apparently harmless pieces of information, when assembled together could reveal a damaging picture.”