The Thumbnail view shows a miniature representation of your process. The section of the process currently showing in the Process Editor is shaded by a blue box. When a complex process cannot be fully displayed, move the blue box in Thumbnail view to display a selected area.
To view another section of the process, click on the Thumbnail view shaded box, and move the box. The corresponding section of the process on the canvas moves into view. The following image shows this shaded box: