Zooming in and out

You can zoom in and out on an aerial photo or map to see more detail or get a larger, big picture view. For zooming, use these keys:

• Zoom in: Press Page Down or the plus (+) key.
• Zoom out: Press Page Up or the minus/dash (–) key. The current zoom level appears in the window title bar, so you always know how far you’ve zoomed in or out.

The zoom level on the window title bar displays the resolution of the image. If the resolution is 4 meters-per-pixel, each pixel (picture element) onscreen represents an object 4 meters in size. (Remember that a meter is roughly a yard.) Smaller numbers mean higher resolution and greater detail. For example, 1 meter-per-pixel resolution means that you can distinguish objects on the ground that are one meter in size. How far you can zoom in and out on an image depends on what type of map you’re viewing.

• Topographic maps: 4, 8, 16, or 32 meters-per-pixel
• Aerial photos: 1, 2, 4, 8, 16, 32, or 64 meters-per-pixel If you’re switching back and forth between aerial photos and topographic maps, use either a 4 or an 8 meters-per-pixel zoom level. This will give you close to a one-to-one size representation of features on the aerial photo and the topographic map.

Moving around the USAPhotoMaps

You’ve probably noticed that USAPhotoMaps doesn’t use scroll bars like other Windows programs. Not to worry; you can still move around in a photo or map by using the keyboard navigational arrow keys:
If you see gray squares while you’re scrolling, map data has yet to be downloaded for that particular area. Figure above shows gray squares with aerial photo data that hasn’t been downloaded. Here are two ways to fill the squares with map or photo data:

• From the File menu, choose Download Map Data➪Fill Screen.
• Press the F key.

USAPhotoMaps connects to TerraServer-USA and downloads the map data for that area.
Instead of scrolling, you can also go directly to a location that you know the coordinates of. Just choose the Go To Lat/Lon item in the View menu and enter the coordinates.
USAPhotoMaps has two display modes: aerial photo and topographic map.
When you download data to fill in the gray squares, only data for the particular
mode that you’re in is downloaded.

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.