Following the attacks on the World Trade Center and the Pentagon on Sept. 11, 2001, the United States rounded up suspected terrorists wherever they were and then moved them to secret prisons around the globe, where they were detained and questioned. The program, largely carried out by the CIA, was known as extraordinary rendition.

Questions about the constitutionality of the program dogged it since its inception.

The UK's Rendition Project believes that there is more that the public doesn't know about the CIA's actions, and they - along with other groups - have been collecting data in an effort to bring the entire program to light. Below is an interactive look at flights the group believes carried CIA prisoners.

The Guardian - where this map was originally posted - has more on the U.S. rendition map: what it means, and how to use it.