Map Basics & Land Navigation (without GPS)

[SkullCollector]

Map Basics & Land Navigation

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Military Grid Reference System

Often, an easy place name is unavailable or a description is too ambiguous, or in fact the party you’re talking to is unfamiliar with the terrain. That’s when you can use grids as a common denominator. Every Arma map has them and they work the same way everywhere.

 

Grids resolve smaller scales the more digits they have. They range from 2-digit, 10 km area grids to 6-digit, 100-metre-accurate positions on an unaided map. Using tools like the MicroDAGR GPS and Vector 21, you can go down to the metre with 10-digit grids, for those times you want to send a JDAM through a window. Most commonly, you will be giving the 6-digit figure.

 

 

So how do you get there?

“Along the corridor, up the stairs.”

 

Your 0-0 point starts in the bottom left corner of the map. From there, you first move sideways to the right along the easting (conventionally bottom) edge to your desired location. This is your east-west position.

 

Then you move up along the northing (or side) edge to finalise the point. This second half is your north-south position.

 

You give this point as a series of digits, called figures. Our flag marker is in grid figures 103-047, but only just.

 

For precision, you can imagine overlaying another grid on any 6-digit grid to get the 8-digit figures. That would put our flag in grid figures 1034-0479.

 

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Scale, Elevation & Contour Lines

The forgotten bottom right of your map shows this:

 

This dynamic hint adjusts to your map zoom level and hands you three pieces of info:

1. Crucially: the contour interval, which tells you the elevation difference between adjacent contour lines (it's in CAPS, so you know it's important)

2. The unit of elevation of the numbers you find scattered across the map

3. A linear scale for measuring distances at each zoom level

 

Using the second bit, we can find hills and valleys at their highest and lowest. You will often hear hills called out as “Hill 123”, which is your cue to look for this elevation number nearby.

However, sometimes you need to know the elevation of a point not specified as such. This is where contour lines help you out.

 

 

Mind our flag marker. To find out where it is, we first look around and find the nearest elevation number. Let’s say 44, east of it.

Then we look at the surrounding elevation numbers and see in which direction they increase or decrease. In this case, they decrease towards the east, meaning east is downhill, and increase west where our marker is, so our flag is uphill from 44.

 

Using the contour interval from our bottom right key, we can simply count the contour lines between 44 and the marker. At this zoom level, each line means we climb 2 metres in elevation. Everything enclosed by two lines is at the same elevation. There are two lines between our reference and the flag, so it’s at 48 metres MSL (= above sea level).

 

The light grey building by the road is one more contour line up at 50 m, but then the next line is a darker colour. Every fifth contour line is higher-contrast, so at this scale, every dark line signals 10 metres of elevation difference from the last. If our scale were 5 m per contour line, each dark line would be 25 m.

 

From here we can discover the second useful property of contour lines: slope gradients.

 

The more space between each line, the gentler the slope. The tighter the lines are together, the steeper the slope. So we can tell: north-east from our flag is a mild downhill, but it becomes a steeper climb the further we go south.

When you see a lot of dark lines packed closely, for example, you are looking at a sheer drop.

 

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Triangulation

Triangulation is finding your position using two (or three) distinct points. Lacking GPS or local knowledge, triangulation is your quickest chance to get your literal bearings and create a reliable, ever-evolving foundation to navigate from.

 

The tools you’re going to need:

- Compass

- Map

- Map tools (ideally)

 

Scenario 1: Stranded

 

Spoiler

You shipwrecked and find yourself on a beach with coarse sand in your everywhere. Your MicroDAGR GPS has found a new home in watery depths. You do, however, have your watertight map pouch and a compass, so let’s see where we are.

 

 

Right away we can spot a fishing village with two piers jutting out. That alone won’t help us, but we can also tell we are in a sort of bay. We bring up our compass and align the sighting post with one of the piers, as such:

 

 

We note the bearing, roughly NW at 308°. This makes the pier our first point for triangulation.

 

On our map, we have a look along coasts for bays and such. We find Baie d’Orange, where we quickly spot a familiar composition of boat-mooring edifices. To confirm that this is our pier, we keep ourselves aligned with it, which will rotate the compass on our map to match our orientation. Indeed, it looks to be it:

 

 

That transparent ruler intruding on this scene is our map tool. You bring it up through your ACE self-interaction on the map screen and navigate to Map Tools – Show Small Map Tool.

 

You can of course use the normal-sized map tool, but it can be a little unwieldy for most infantry-scale uses. It will spawn in the bottom-left corner of the map, from where you can drag it to where you need it.

 

As long as we are still aligned with our reference point, the pier, and with the compass still sighted on it, we can navigate to the ACE self-interaction – Map Tools menu again and select Align Map Tools with Compass. With that done, the red arrow in the map tool’s centre circle that previously ran straight through North now intersects a bearing of 308°, just like our compass. Now we can move its ruled edge over the pier and draw a long line along it, holding down Ctrl and left-click while keeping to the ruler. Don’t worry if it’s jiggly, it will straighten itself out:

 

 

The eagle-eyed among us will extrapolate where we are, but let’s carry on.

 

On the map we spotted another pier. Turning right, indeed, there it is:

 

 

Using the same method of sighting down the compass…

 

 

… and aligning the map tool with it to draw a line: 

 

 

We have successfully triangulated our position at the line intersection.

 

As a last step, we can increase our confidence in this location by looking for confirming references near us. On the map, we can see there is a rock formation marked next to the intersection of our red lines.

 

Turning left, there it is:

 

 

 

After mere minutes of looking around us, we can relay our position as in grid 112-019, or at least get moving with confidence to where we can.

 

 

Scenario 2: Organising Support

 

Spoiler

 

With our newfound skills in triangulating our own position, we can also start triangulating for others far away.

 

We get a radio call from a patrol asking for CASEVAC. Their team leader took a bullet to the plate carrier through the pocket that kept his MicroDAGR, and the panicked recruits skipped their land nav courses.

 

“Crossroads, Rover 2-2. We moved East from the temple ruins, we’re now on a rocky peak above the jung- oh god, he just coughed up bloo-“

 

Looking at our own map, we remember where the temple ruins are. Having a look east of it:

 

 

There are a lot of rocky peaks, so this much information is not yet useful enough to organise help.

 

We radio back: “Rover 2-2, Crossroads. Have a look around for landmarks. What is their bearing to you? Over.”

 

“Crossroads, there is a radio tower to our 95°, like a klick away?”

 

With that info, we can move our map tool over the radio tower we find east of the ruins, so that the locating hole central to the compass circle lines up with the map marking. Now hold Alt and drag the outer bit of the tool until the red line crosses 95°.

 

 

Crucially, we only know the bearing from the observer. The reciprocal of that bearing is where the observer is from this point. Just as south is 180° from north, reciprocal bearings are 180° apart. To find the reciprocal, add 180° if the initial direction is less than 180°, or subtract 180° if it's more. 

 

In our case, Rover 2-2 is at 275° from the radio tower.

 

Move up the map tool so the ruled edge lines up with the tower and draw a long line:

 

 

We now radio back to ask for a second reference landmark.

“Crossroads, yeah, there is a plantation south of us. It has a water tower and a windmill?”

 

With that info, we can immediately pinpoint their location: 

 

 

“Rover 2-2, Crossroads. Your location is in figures 121-086. CASEVAC is on its way, sit tight. Out.”

 

 

Map Tools: Bonus

Spoiler

 

 

The map tool is an unassuming little fellow quickly proving to be your friend in all things land nav.

 

1. Centre alignment

   1. Put this on your point of interest (POI) to make it a reference

   2. Rotate the tool by holding Alt and dragging the outside around

2. Alignment line

   1. This red line intersects all points at a given bearing

   2. With the centre alignment on your position, align the red line with a remote POI to get its bearing

3. Bearing (degrees)

   1. The bearing in degrees (360° in a circle)

   2. Fits all your infantry needs

4. Bearing (milliradians)

   1. The bearing in milliradians (mils, 6400 in a circle¹)

   2. When you need high precision, e.g., call for artillery fire

   3. Note: The graduation is given in hundredths, so add 00 to the number you read

   4. At 1000 metres, 1 metre is 1 mil

5. Ruler (kilometres)

   1. Hold Ctrl-LClick and draw along the ruled edge to make a thick straight line

6. Grid coordinate scale

Remember the grid we had to imagine over a 6-digit grid to get 8 digits?

This square scale helps us pinpoint these precise coordinates without the use of GPS and without risk of misjudging your inner eye.

 

If you are given coordinates and want to find them on the map:

1. Align the 0 0 point with the bottom left (south-west) corner of your area grid (the scale will be “open” towards the grid south-west of your target grid)

2. Physically move the map tool to the right until the top rule intersects the vertical grid line with the mark corresponding to the first coordinate figure the map does not resolve

3. Physically move the map tool up until the side rule intersects the horizontal grid line at the first figure your map does not resolve

 

If you want to find the coordinates of a point you see on the map:

1. Move the 0 0 point over your POI

2. Read along the horizontal rule to the left until a mark intersects the vertical grid line; the numbers are your 6-digit figure and count each tick mark between the numbers 0 to 9 for your 8-digit figure

3. Read down the vertical rule until a mark intersects a horizontal grid line; note the marks as before

 

On the small map tool, the numbers represent 100 metres and each minor tick mark 10 metres.

On the normal map tool, the numbers still represent 100 metres, but each minor tick mark is now 20 metres (and is therefore no use in determining 8-digit grids).

 

 

¹The military expresses a circle to 6400 mils; mathematicians roll their eyes, knowing it's 6283

 

 

 

 

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To see what silly things I might eventually do with formatting, here's the GDocs link:

https://docs.google.com/document/d/1CvcM2uJ7ANaKmnalOIUOS3brFQNdRxg-Q-0jIRMhs8o/edit?usp=sharing

[SkullCollector]

Addendum: Keypad‽

 

When you need more precision than the 100 metres a 6-digit grid can provide, you have another option: Keypad, kp.

 

If you play Squad or the old Project Reality, you might have encountered keypads already.

 

The point to the keypad method is immediately apparent when you look down at your keyboard, at least if you have a numpad. Instead of further 10x10 grids for 8 digits, it divides a grid into 9 squares. That's still plenty accurate for navigation, and even for artillery.

 

So why faff about with overlaying grids in the first place? The keypad is an elegant solution. It builds on familiarity with an every-day object. Its problem is as annoying as Apple refusing to use USB on their phones: mixed convention.

 

 

In real-life orienteering, the convention is to use a phone keypad, because unlike us gamers, a soldier will more likely have a radio or sat phone than a keyboard. (It's also what the boy scouts taught me.)

Their numbers start at 1 in the top left and end at 9 in the bottom right.

 

Our numpad starts at 1 in the bottom left and ends at 9 in the top right.

 

So is the flag marker in figures 103-047 kp2 or 103-047 kp8?

 

For the very simple reason that we have a numpad in front of us at all times (unless you're tenkeyless, RIP), most games and gamers teaching gamers will default to the numpad order. When you do use this method, say your grid and numpad [n], instead of keypad.

But you cannot be sure.

 

I would advocate that we familiarise ourselves with the grid system and use 8-digit grids for precision. They feed directly into other gadgets we have available, such as the MicroDAGR.

For artillery, being off by one or two grids at this scale will rarely change the outcome (because field cannon dispersion is about 30 metres).

For navigation, you also orientate yourself by your surroundings and can use communication to pinpoint a location, so again, a couple grids won't do harm.

 

In contrast, mixing up keypad 2 and keypad 8 can mean the other side of a town, topographic feature or minefield.

[Noah_Hero]

Do note that there are Arma maps that for example have a flipped vertical Axis, i.e. (000,000) is the top left instead of the bottom left (e.g. Sahrani once you zoom into 6-figures). In these cases you obviously have to change the vertical axis orientation of your 8-figures as well, as they're refining the overall map-gridding and are therefore dependant on its orientation. The Numpad or Keypad however stay the same, as they're not actually dependant on the overal gridding, since they're based on your keyboard or telephone and that looks the same no matter what map you're looking at.

[Lindi]

...now try doing it under fire!

Great work explaining this, should really brush up on my maps skills. I'm just way too used to GPS and/or bluefor markers.

[Noah_Hero]

On 5/3/2021 at 11:26 PM, SkullCollector said:

Note: Unfortunately, the marks are inverse to how you read grids, so flip them

Technically you can make it correct if you just turn the map-tool to 180°. The numbers for the horizontal axis are upside down then but the gridding correct again.

And as we figured out earlier that there are maps with weird axis: If both axis are inverted the gridding is correct when the map tool is turned to 0°, if only one of the map axis is inverted, you can turn the map-tool to either 270° to accomodate for an inverted vertical axis or to 90° to accomodate for an inverted horizontal axis.

[SkullCollector]

2 hours ago, Noah_Hero said:

Technically you can make it correct if you just turn the map-tool to 180°. The numbers for the horizontal axis are upside down then but the gridding correct again.

And as we figured out earlier that there are maps with weird axis: If both axis are inverted the gridding is correct when the map tool is turned to 0°, if only one of the map axis is inverted, you can turn the map-tool to either 270° to accomodate for an inverted vertical axis or to 90° to accomodate for an inverted horizontal axis.

 

This is true and a good tip, I've added inverting the map tool to that line.

The real purpose of the right-angle scale is for measuring towards a coordinate, not sub-graduation. When you are given an 8-digit (or 10-digit) grid, you would align the 0 in the top right with the south-west (bottom left) corner of the grid. Then you look at your figures, say: 0507 0445. Our maps go to 6-digits, so we can find grid 050 044 and put our 0 in the corner. Then we physically move the tool 7 minor tick marks along the easting to the right. Then we move it 5 minor tick marks upwards along the northing. Now our 0 is exactly on the location of our 8-digit figure.

 

I didn't think going that deep would be useful, but I'll add it to the guide.

 

The grid axes flipping, however, is hopefully a sign of rare bad map design and should not be taken as convention, so I won't include it in the guide. The awareness is good, though.

00 should always be in the south-west corner if it follows MGRS.