There are many variables to land navigation. Such as declination, the offset of true and magnetic north. When using a map, there are variables like the survey used to make the map. Maps are not 100% accurate either, particularly manmade objects are always out of true scale. When using a GPS, there are the variables such as matching the survey Datum to that of your map, you could be miles off if not set correctly. GPS devices often suffer accuracy in dense woods and in narrow canyons.
You have to learn how to plot GPS information to your map to correctly plot where you are. There are a variety of method available and most need special plotting tools to accurately plot a position to your maps. Maps vary much in scales, each part of the world may be scaled differently, depending on who printed the map.
A pace counting technique should be employed and you must know how many paces you take to travel 100 meters, in uphill, downhill, flat terrain. One persons count will differ vastly to another persons. A counter should be used to keep an accurate count of paces. In the SF we used "Ranger beads", or if being quiet is not important, you can use little mechanical counters. Not each pace is counted on the counter ot beads, perhaps each 10. Example, for me 60 left foot hits is my pace count for 100m on flat ground. I would count 10 left steps, that is ONE on my counter. when I reach TEN on my counter, I have traveled 100m on flat terrain.
All navigation depends on knowing your starting point. A good technique is to use "deliberate offset" to reach a specific point. Say you are trying to navigate to a trail junction, a "T", from a dense forrest. Make a point to deliberately navigate to one of the trails, left or right of the junction and then travel the trail until you reach the junction. Remember, manmade objects (trails, roads, buildings) are not true scale on a map!
There are many good books on navigation with map and compass and GPS and should be read until understood and navigation needs lots of practice in the field. Once you master it, you should keep practicing. It is easy to forget a step or mis plot a destination and get off track.
Some compasses have a feature called delination adjustment built in. Say your map has a declination of 15 degrees East from true north. You can preset that into the compass so plotting on the map already accounts for the variation in magnetic to true north when using the compass to follow. These compasses are great, except when you forget to change the settings or set it backwards. You could easily be 30 degrees off the desired course if the compass was set 15 degrees West delination and your map is 15 degrees East declination! The reason they put a mirror on that type compass is so you can readily see who is lost
I do use one of these compasses, they are the best. I have a military model that does not come with the adjustment feature. Better to do the math and double check it. Always carry a pencil and paper for notes, etc.
Keeping track of where you have been is also important, look back often and remember key terrain features. This usually is not much help in dense wood or jungle but should not be overlooked, There is usually some feature that stands out and can be used for orientation.
Some recommended reading:
Be Expert with Map and Compass by Bjorn Hijellstrom
U.S. Army Map Reading and Land Navigation Handbook
Gps Made Easy: Using Global Positioning Systems in the Outdoors by L. Lethem
The Wilderness Route Finder by Calvin Rutstrum
Good websites:
http://www.wildernessmanuals.com/manual_1/index.html
http://www.maptools.com/
I hope some of that helps. Cheers!
