The canvas
This is the main working area of the editor. You can add, move, resize, and tweak any control added to the canvas. Check out Adding and Arranging UI Controls to learn more.
The canvas is large - it's 20000px x 20000px - and flexible so you can scroll in every direction to make room for bigger wireframes or more controls if you need to.
When you zoom in or out, the Mini-map appears to help you navigate large wireframes with lots of screens or pages.
Note: If you are working on a small screen or have very large wireframes you might want to check out this section on hiding the panels to make more room for the canvas.