Navigation Zone

From ZBrush Info

The Navigation Zone is the outside area of the canvas bordered by a thin white line. Position the cursor within this zone to move, scale or rotate your model when your model fills the canvas and so there is no background area available.

The Navigation Zone is only available in Edit mode and when the canvas is larger than the visible area. When the canvas displays in its entirety so that there is a border around it, the border area can be used in the exactly the same way as the Navigation Zone. Scrolling the canvas so that the border area appears can be useful for some operations.

To force a Navigation Zone to appear, simply increase the size of the canvas by changing the values in the Document: Width and Height sliders and pressing Resize. You can store this new canvas size as a default by saving a Startup Document.

To Learn About The Startup Document Click Here.