When your 3D chart comprises columns of various heights, chances are that some of the columns hide other columns placed behind them. This is especially true with 3D charts that have a Z axis. One of the ways to make the columns placed behind visible is to make the taller columns transparent. The other way to solve this issue is to rotate the 3D chart so that you end up with a view in which the shorter columns become clearly visible.
Learn how to rotate 3D charts in PowerPoint 2011 for Mac

