How Big Is the U.S. Debt?

For more details on the total Federal debt, start on slide 35 of this PowerPoint presentation: http://www.antolin-davies.com/presentations/ihs11a.ppt
Economics professor Antony Davies illustrates the size the U.S. federal government's debt and unfunded obligations. He breaks down the total U.S. debt and obligations into parts and compares them with the size of the GDP of countries around the world, showing the magnitude of America's fiscal situation.
Want to give that graph a closer look? Prof. Davies has made it available on his website here:
http://www.antolin-davies.com/conventionalwisdom/governmentdebt.pdf