Recent debate over U.S. government surveillance has focused on the information that American technology companies secretly provide to the National Security Agency. But that is only one of the ways the NSA eavesdrops on international communications.

A classified NSA slide obtained by The Washington Post lists “Two Types of Collection.”

One is PRISM, the NSA program that collects information from technology companies, which was first revealed in reports by the Post and Britain’s Guardian newspaper last month. The slide also shows a separate category labeled “Upstream,” described as accessing “communications on fiber cables and infrastructure as data flows past.”

The interaction between Upstream and PRISM — which could be considered “downstream” collection because the data are already processed by tech companies — is not entirely clear from the slide. In addition, its description of PRISM as “collection directly from the servers” of technology giants such as Google, Microsoft and Facebook has been disputed by many of the companies involved. (They say access to user data is legal and limited.)

However PRISM works, the NSA slide makes clear that the two collection methods operate in parallel, instructing analysts that “You Should Use Both.” Arrows point to both “Upstream” and “PRISM.”

The overall heading of the slide is “FAA 702 Operations,” a reference to a 2008 law that enabled, without an individual warrant from a court, collection on U.S. soil of communications of foreigners thought to be overseas, including when the foreigners are communicating with someone in the United States. The law says the collection may be for a foreign intelligence purpose, which includes terrorism, nuclear weapons proliferation or cyber-security.

The slide also shows a crude map of the undersea cable network that carries data from either side of North America on to the rest of the world. As a story in Sunday’s Post made clear, these undersea cables are essential to worldwide data flows and to the surveillance capabilities of the U.S. government and its allies.

This slide bears many resemblances to one published by the Guardian on June 8, shortly after the initial disclosures about PRISM. That said, the Guardian’s slide shows an undersea cable map of most of the world. The one obtained by the Post shows mainly sections of North America. It is not clear why the slides vary in this way.

Both slides have circles attached to arrows suggesting possible collection points, but they cover areas too broad to discern where NSA accesses fiber-optic cable networks. The slides also list code names under the Upstream program.

The Post version lists Fairview, Stormbrew, Blarney and Oakstar yet does not describe any of them. The Guardian slide lists Fairview and Blarney, with two others blacked out.

The Post has previously reported that Blarney gathers up metadata – describing who is speaking to whom and through what networks and devices – as data flow through the Internet’s backbone.

For Sunday’s story, the Office of the Director of National Intelligence issued a statement defending its collection methods as crucial to protecting national security.

“As always,” the statement said, “the Intelligence and law enforcement communities will continue to work with all members of Congress to ensure the proper balance of privacy and protection for American citizens.”

Reporters Ellen Nakashima and Barton Gellman contributed to this report.