Understandably, many people have a hard time differentiating the Central Intelligence Agency from the United States other intelligence agencies like the NSA (National Security Agency) and the DIA (Defense Intelligence Agency). All three of these mediums deal with foreign intelligence and big data. In most simplistic terms, all of their purposes are all to collect and analyze data for American security. Both the National Security Agency and the Defense Intelligence Agency are under the control of the Department of Defense, which plays a large role in the data that they are collecting. They could be compared to more centralized versions of the CIA, because the CIA does not just focus on the defensive aspect of foreign affairs. “The main difference between the NSA and the CIA, FBI and DIA revolves around how each agency gathers its intelligence information. The NSA does not have field agents who do in-person intelligence gathering who travel the globe like 24’s Jack Bauer. Instead, its employees work primarily in Fort Meade, MD with a smaller work site in San Antonio, Texas” (Levy).
CIA, NSA, DIA – Comparison of Big Data / Intelligence Agencies
CIA 
I find this analysis of all the intelligence agencies to be very helpful to people reading about the CIA for the first time. It provides information on what kinds of data each agency collects and what they use this data for.
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