An important aspect of using a topo map is the fact that you can pin-point a location on the earth, transpose that location onto the corresponding map with fair precision and then communicate that location to others. This allows you to locate and share items such as link-up points, caches, targets, en route rally points, etc. The most efficient method is the grid reference system.
I won’t go into a detailed topo map discussion here, Max Velocity’s already done that on his site with an excellent primer. He explains how to locate a point on any 1/25,000 OR 1/50,000 topo map using the Military Grid Reference System (GMRS). If you are attending his course he has written that this is the map system he will use. He goes on to write that you can buy any USGS topo map with the GMRS grids pre-printed on your personalized map at mytopo.com. I have ordered maps from them and I highly recommend them.
For those folks who already have a stock of USGS maps that are 1/24,000 maps, have the ability to print their own maps or have compasses in 1/24,000, I will explain how simple it is to draw a grid system on your map. The following is taken directly from maptools.com:
All USGS topographic maps printed in the last 30 years or so include UTM grid tick marks, in blue, on the margin of the map. For a short time period after 1978 the USGS was printing a fine lined UTM grid on their topographic maps. They have since discontinued this practice.
Since most USGS 1:24,000 scale topographic maps do not have grid lines printed on them, you will need to draw them in by hand.
Start by finding a flat surface to work on. Use a straightedge that is long enough to draw a line across your map. Two to three feet long is a good length.
Line the straightedge up between two corresponding UTM tick marks along the neat line (the edge) of the map. Remember that UTM grid lines are not exactly North-South or East-West anywhere but in the center of a zone. This means that the grid lines will not be parallel to the neat lines.
Using a mechanical pencil or a fine pointed pen draw a line between the two tic marks. If you are using a pen, select one that has waterproof ink. In addition, you will want to use a straightedge that has the edges lifted off of the paper. This will help keep from leaving an ink smudge when you move the straightedge. High quality straight edges will often have a thin piece of cork stuck to the bottom. This helps keep the rule from slipping, and keeps the edge off of the paper. A piece of masking tape centered on the bottom of your straightedge will work also. Occasionally wipe of the edge of the straightedge to avoid any ink build up.
Gridding maps is tedious work. We all wish the USGS would go back to printing the grid on the map. But even then, we would still need to grid our existing maps. As you can see this is not the kind of thing you want to do on the hood of a truck or using a flat rock. Grid your maps before you need them in the field! In a pinch you can fold the map over on itself and use the edge of the paper as a straightedge.
A couple of items that bear repeating; the outside map margin or border is known as the “neat line” and the UTM grid tics are tiny, blue lines that extend out from the border (or neat line) on each side, top and bottom. Insure that when you draw in your lines that the UTM grid tic mark numbers match top to bottom or side to side and they are all parallel to each other. When you are finished you will have a matrix of squares filling in your map. Some of the grids along the margin might not be complete squares, until you join up adjoining map sheets with grid squares drawn on them also.
The squares you have drawn are one thousand meters across or in other words, one kilometer. Or as we said in the Army, one “click”.
Now you can use the scales on your 1/24,000 compass base to locate items up to 100 meters.
Another nifty tool I always carry in my map case is the Brooks-Range All-in-one Map Tool Pro. Google it and blow up the picture on your computer. It has every scale I’ve ever used and some I haven’t. It also has your grid reference tool for 1/24,000 maps that you just lay over your map. It also contains slope indexes along the bottom that you can lay over the contour lines on any map and it will give you the corresponding incline. It also has a compass rose in the middle surrounding the grid index. If you gut a piece of 550 cord, pierce the very center of the compass rose intersection with a needle creating a tiny hole just large enough to feed one of the 550 strands through, tie a knot on the strand on the front side of the tool, then pull the strand through the hole in the tool until the knot tightens against the front of the tool. When you are finished you can lay the tool on the map, north pointing to the top of the map, with the center knot over your present location, turn the tool to align the map tool edges or grid lines with the grid lines you have drawn on your map, then pull the strand around until it intersects your target on the map. You can then read the direction or azimuth in degrees to your target off the compass rose on your tool. No need to draw lines on your map or to even lay your compass on the map. Now set your azimuth into your compass, keeping in mind the declination offset (unless it is built into your compass) then move out and draw fire.