Land Navigation Basics

Fitness gets trained for a year; land navigation gets crammed the week before and then ends people's courses. It is a learnable skill with maybe six components, and none of them are hard on their own.

Reading a grid coordinate

Military maps use MGRS. The rule that never changes: read right, then up. Easting first, northing second, always.

An eight-digit grid such as 4281 6754 splits into an easting of 4281 and a northing of 6754. The first two digits of each are printed gridlines on the map; the second two are tenths of a grid square, measured with the protractor. More digits means more precision:

A standard 1:50,000 map has grid squares 1,000 metres on a side, which on that map is two centimetres. Everything in the next section follows from those two numbers.

Plotting a point with a protractor

This is a mechanical procedure. Done slowly and identically every time, it does not fail.

1. Find the grid square from the first two digits of each half — easting 42, northing 67. The square is the one whose lower-left corner carries those lines.
2. Lay the protractor's coordinate scale inside that square, keeping the horizontal scale parallel with the horizontal gridline.
3. Slide it right until the vertical scale reads your easting tenths — 81 — against the left-hand gridline.
4. Slide it up until the horizontal scale reads your northing tenths — 54 — against the bottom gridline.
5. Mark through the protractor's corner hole with a fine point. Then check it: does the mark sit where the terrain around it makes sense?

Terrain features

Contour lines are the whole map. Five major features, three minor, two supplementary — the ones worth knowing cold:

• Hill — closed contours, high ground in every direction from the top.
• Valley — contours in a rough U or V pointing uphill, usually with water in the bottom.
• Ridge — contours in a U or V pointing downhill; high ground running in a line.
• Saddle — the dip between two areas of high ground. The single most useful navigational feature there is, because it is unmistakable on the ground.
• Depression — a low point, marked with tick marks pointing inward.
• Draw — a small valley; ground slopes down toward it from three sides.
• Spur — a small ridge coming off the side of a hill.
• Cliff — contours that touch or run together.

The mnemonic people remember is that contours pointing uphill mean water runs through it. Draws and spurs alternate around a hillside, which is why counting them as you traverse is a reliable way to know where you are.

Azimuths and declination

An azimuth is a bearing in degrees from north, 0 to 360, measured clockwise. The complication is that there are three norths, and two of them matter:

• Grid north — the vertical lines on your map.
• Magnetic north — where the compass needle actually points.
• True north — the pole. Largely irrelevant to you on the ground.

The angle between grid and magnetic north is the G-M angle, printed in the declination diagram in the map's margin. Convert in the direction the diagram tells you — over a few kilometres, ignoring a ten-degree G-M angle puts you several hundred metres off your point, which is the difference between finding it and walking past it in the dark.

A back azimuth is your azimuth plus 180 degrees (or minus 180, if adding would take you over 360). It is how you check that you are still on line by sighting back at where you came from.

Pace count

Your pace count is how many times your left foot hits the ground over 100 metres. Most people land somewhere between 60 and 68.

1. Measure a known 100 metres. A football field, end line to the far goal line, is close enough to start.
2. Walk it at your normal loaded pace and count left-foot strikes. Do it four times and average.
3. Then measure it again uphill, downhill, at night, and through thick vegetation. Every one of those numbers is different, sometimes by ten or more.
4. Write all of them down and carry them. Nobody remembers five numbers at 0300.

Track the count with pace beads or by moving a pebble between pockets each hundred metres. Counting to fourteen hundred in your head while doing anything else does not work.

How to actually find a point

Beginners shoot an azimuth at a point 1,500 metres away and walk. It almost never works, because small errors compound and there is nothing to tell you they have. What works:

1. Plan the whole leg before you step off. Distance, azimuth, what terrain you will cross, what you will see on the way, what tells you you have gone too far.
2. Pick an attack point. Some unmistakable feature — a road junction, a saddle, a stream bend — within about 300 metres of your objective. Navigate to that with confidence, then run a short precise leg from it.
3. Use handrails. A road, a fence line, a stream running roughly where you are going is faster and more reliable than a compass bearing through woods.
4. Set a catching feature. Something across your path beyond the objective — a road, a ridge, a river — that tells you unambiguously that you have gone too far. Without one you will search forever in the wrong place.
5. Aim off deliberately. If your point sits on a stream, aim fifty metres to one side on purpose. When you hit the stream you know which way to turn. Aiming straight at it leaves you guessing.
6. Use steering marks. Shoot the azimuth, pick a tree or rock on that line as far ahead as you can see, walk to it without watching the compass, repeat. Far more accurate than staring at a needle.

Night

Everything above gets harder in the dark, and the compensations are specific:

• Your pace count changes. Measure it at night or you are guessing.
• Terrain association mostly stops working. Dead reckoning carries more of the load, so your azimuth discipline has to be better, not worse.
• Distances feel far longer than they are. Trust the count over the feeling.
• Protect your night vision — red or blue-green light, briefly, hooded. One flash of white light costs you twenty minutes of adaptation and your point is now further away than it was.
• Plot everything in daylight if you get the chance. Plotting a fresh grid by headlamp in the rain is where wrong-scale mistakes happen.

Questions

Related: preparing for SFAS · the SFRE route · building the 12-mile ruck