Magnifying
Glass
The Magnifying Glass lets you zoom in and out on any point in the Top View. Clicking on the Magnifying Glass button makes the cursor turn into a magnifying glass with a plus sign in its center when the cursor is in the Top View.
To zoom in on a particular spot, click the Magnifying Glass on that spot. If this doesn't bring you in close enough, click again.
To zoom in on an area, click and hold on one corner of the area with the Magnifying Glass. Drag across the screen until you've selected the area you want in a rectangle. Click again. (If you've selected an area and then decide you don't want to zoom in after all, right-click instead and choose Cancel Tool.)
To zoom out, hold down the Shift key, which turns the plus sign into a minus sign. Click the Magnifying Glass on the spot where you want the Top View centered. If this doesn't take you out far enough, hold down the Shift key and click again.