What's panning? Panning is another way of describing scrolling, only a little different.
When you've zoomed in on the treemap, it's not unusual that you'll see something on the edge of the window that you'd like to see in more detail. Panning is a term that comes from movieland, and it means to take the camera and slowly turn it to show more of the scene to the left, right, up, or down. (SpaceMonger uses an imaginary camera hovering over your data, and you too can zoom in and out just like a camera, and move left and right too; so it makes more sense to call it "panning" than to call it "scrolling".)