And redacted they are. Under the law, federal agencies are required to give a yearly review of how they responded to requests under the act. That data includes statistics on why an agency decided to hide information; the agencies are allowed to keep information away from the public by citing one of nine exemptions .

How can that change? Recently, Congress has held hearings on transparency in the Freedom of Information Act — a tool citizens and journalists use to request information from the government. If you’ve ever seen a government document with redactions, you might have some experience.

But almost no one thinks government information is getting through. The survey found only 11 percent of adults believed there was effective sharing of information at any level in government.

The exemptions range from the broad (privacy) to the deeply specific (geological information on wells). But when you see that data charted — like we have for nine prominent agencies here, using the most recent data, from 2014 — you start to see patterns. The Department of Justice loves law enforcement secrets; the EPA has fewer geological well secrets than the Department of Defense. CIA information, you will not be surprised to learn, is often classified.

A few notes about what you see. The percentages in the chart are measured against the nine agencies listed, not against all agencies bound by FOIA, of which there are many more. It should also be said that the data presented here doesn't factor in the size of the agencies: the Department of Defense dominates the list of secrets, but it’s also a sprawling organization fielding many, many requests, and thus has more opportunities to exempt information. But the end result is still, hopefully, a useful qualitative look at what you’re not allowed to see.