Use the roller wheel on your mouse to zoom in or out. Additionally, hold down on the Shift key and then click and drag to create an extent box to which the site will zoom. Double clicking on the map will ONLY zoom in on the map on which you double clicked. Clicking while holding down the mouse button and dragging will move the maps accordingly. You can always synchronize the scale and location of the maps by clicking on the blue "Scale" or "Location" buttons at the top of this column.