The All Topo viewer can help you triangulate a feature’s location if you know the bearing to the location from two separate known locations.

Consider a forest fire burning some distance away. You can see the smoke, but you have no idea how far away the fire might be. If you have a GPS and a compass you can quickly determine the fire's location:

1 From the first place you can see the fire, take a GPS reading and a compass bearing. Make a note of the bearing and your GPS location:

40° 51' 13.81" N, 109° 5' 3.90" W
97.5° magnetic north

2 Drive to a second location, far enough away that the compass bearing changes appreciably, again note the bearing, and GPS location:

40° 51' 13.81" N, 109° 2' 36.65" W
223.5° magnetic north

3 Finally, display the 'Triangulation Tool' by selecting 'Tools: Triangulation…' from the main menu:

Enter the two base coordinates and angles, selecting the correct North Reference (Magnetic North).

All Topo will compute the fire location and place a temporary marker at the intersection. Press the thumbtack next to the triangulation point to add a user annotation at the intersection.

It is important to choose observation points that have a large difference in bearing to the target, and to use a quality compass in a non-magnetic environment. In this example, a 2 degree error in the bearing results in a ¼ mile error in the projected fire location. For this reason, the use of a quality sighting compass like the Brunton Sightmaster is highly recommended.

The Brunton Sightmaster (SM360LA)

With some practice, you can quickly take ½ degree repeatable bearings with this compass. Since All Topo automatically adjusts for declination, you won't need to worry about computing declination (or in the worst case setting the declination backwards!)