Switching between aerial photos and topographic maps

After you know where you are in a photo, look at the commands that you can use to move around. As I mention earlier, TerraServer-USA provides both aerial photos and USGS topographic maps,and USAPhotoMaps lets you switch between the two types of images. (Figure above shows a topographic map.) This is useful because you can look at a topographic map and then immediately see what the same location looks like as an aerial photo. This is a big advantage because aerial photos often show more feature detail than topographic maps.
Here are the two ways (in USAPhotoMaps) to display a topographic map version of an aerial photo you’re viewing:

• From the View menu, choose Map Type➪Topo.
• Press the T key.
• If gray squares appear onscreen, you haven’t downloaded map data for that area yet. To download the map, press the F key. To switch back to an aerial photo view of the location
• From the View menu, choose Map Type➪Photo.
• Press the P key.