From User Guide
Its a common problem with diagrams to grow big and make it harder for the user to view it easily without scrolling around. The Thumbnail View allows you to see the whole diagram in a compact form to make it more accessible. To access the Thumbnail View follow these steps:
1) Go to "Window > Show View" and select the option "Other..."
2) Select the "Thumbnail View" in the "Architexa" folder.
3) The view window should now be visible and you should be easily inspect any part of the diagram by simply dragging the highlighting box over the compact diagram shown in the Thumbnail View.