Defining Regions to Download

BackCountry Navigator allows you to start a download by defining regions on the map screen and then choosing from topo maps, aerial photography, and urban areas color photography, where available.

While the method of choosing a center point and size still works, you are able to better define an area for download by making selections on the map screen. This is the preferred way to start a download. When doing this, it is helpful to define some points of interest first. 

If you don’t already have known coordinates in order to define some waypoints, the easiest thing to do is add USGS Places through the placefinder. You can reach this by using the Find button on the Data Page.

Here I’m looking for a spot, Paradise Point State Park, WA, that I know is a few miles up the Lewis River. When I select this on the list and choose okay, the place is added to the map. I can repeat the process and find the Lewis River as well.

For ease of use I zoom out until I can see them both, and turn on Labels for Places. I then use the Action-> Select -> Type menu to change the selection type to Rectangles. With a few taps on the screen, i define some overlapping rectangles.

I can then choose Action->Select->Download Maps, which brings up the Download Region dialog.

The maps available are public domain imagery from Terraserver-USA. You can use any valid internet connection to download. The most common are:

  • Data service from your cell phone provider: this is often the most expensive, and slower than other methods, but is available at your
  • Wifi network: This is a higer bandwith connection available form your home network or an internet hot spot.
  • Connection to Internet Connected Computer:  This is common, easy and cheap. Downloading while connected via cradle or cable will use your computer’s internet connection.

The types of maps you can use are:

  • Topo: These are USGS topographical maps equivalent to the paper maps at 1:250K, 1:100K, and 1:24K scales. This imagery is available in virtually all parts of the US up to 4 meters per pixel.
  • Aerial: These are black and white aerial photographs, available in most parts of the US up to 1 meters per pixel.
  • Urban: These are detailed color photography, available in select metro areas in the United States, up to 0.25 meters per pixel.

To see the availability of these image layers, see the coverage map at http://www.terraserver-usa.com/.

You can also choose the level of detail – and how fast you want to use up your storage card with the map data:

  • 4m: Uses approximately 64K per square mile
  • 1m: Uses about 512K per square mile.
  • 1/4m: Uses about 8 Megabytes per square mile, when available.

Once you’ve made your choices and pressed the Start button, the dialog will count up to the number of tiles needed, then show the progress as it downloads them. Each tile uses up approximate 8K in your database file. If an area does not have a certain imagery, such as Urban tiles, then you will see it count back down to zero as shown on the right.

 

You can now see that you have both topo and aerial imagery downloaded.

If you pan to the edges of the region you defined, you see that it fades from the higher res imagery to the lower res imagery. This is normal and due to the way these tiles overlap in multiresolution views.