On the left side of the Schematic View, below the list of background maps, you will find the inset schematic. This small schematic always shows your complete area, and may be used to zoom in and out of the display on the main schematic. The area currently shown in the main schematic is indicated by a red box on the inset schematic. Click and drag on the inset schematic to change what is shown on the main schematic. You can also move the zoom bar (below the inset schematic) or use the mouse wheel to zoom in or out (ctrl+mouse wheel will zoom in and out faster).