Map Basics & Land Navigation
--- --- ------ --- ------ --- ------ --- ---
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.
--- --- ---
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:
Crucially: the contour interval, which tells you the elevation difference between adjacent contour lines (it's in CAPS, so you know it's important)
The unit of elevation of the numbers you find scattered across the map
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.
--- --- ---
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:
- Map tools (ideally)
Scenario 1: Stranded
Scenario 2: Organising Support
Map Tools: Bonus
--- ------ ------ ---
To see what silly things I might eventually do with formatting, here's the GDocs link: