This tutorial is intended to provide the basics of communicating information on a map by the use of a standard grid reference system. The system can describe a location at the level of accuracy desired by the user. The most common are to within 1km (4 figure grids), within 100m (6 figure grids).

Greater accuracy can be written into the grid system, but it becomes a question of whether the extra accuracy of the grid serves any purpose. For example a 12 figure grid describes a location to within 0.1m, but seriously, in military terms knowing where something is to the nearest 10cm is overkill.

Note: The mapping system about to be described uses metres as the standard measure. Sorry USA and UK - you're just gonna have to catch up with the rest of the world.

The world is divided into 1000x1000m (1km x 1km) gridsquares, defined by gridlines with numbers 00 to 99. Each of these gridsquares can be further subdivided into 100 squares of 100x100m. Each of these 100mx100m squares can be further divided into 100 10mx10m squares, and so on.

All co-ordinates are read in the "right, then up" method. That is, the origin (00 00) of the overall co-ordinate system is in the SW corner of the area mapped. Thus, all co-ordinates indicate first the "Easting" (how far east of the origin, moving to the right on the map), then the "Northing" (how far north of the origin, moving up on the map).

Map 1: Wellington City (1:50,000 2cm = 1km) Click to Enlarge

As a specific example, Point Jerningham on Map 1 above is located at Grid 61068965. Grid co-ordinates ALWAYS contains an even number of digits, either 4, 6, 8, or 10. When reading the co-ordinate, you divide the numerical part in half; the 1st half is the easting, the 2nd half is the northing. In this case 61068965 separates into 6106 and 8965. Within each section of the co-ordinate, the following rules apply:

a. The 1st 2 digits in each section represent the last 1000m gridline you come to without going beyond the desired point as you move either right or up on the map. They define the 1000m square which contains the desired point. If you just used 4 digits for the co-ordinate in this example, they would be 61 and 89. These numbers are written along the margins of the map, labeling actual 1000m gridlines.

Starting on the western side of the map, go to the right until you find vertical gridline 61, then go up it to horizontal gridline 89. Their intersection defines the 1000m gridsquare 61 89, which by convention is the square NE of the intersection. This makes the gridline intersection the "origin" for all further digits in the overall co-ordinate, which specify where in this square you're talking about.

b. The 3rd digit in each section represents how many 100m segments beyond the gridline you continue moving right or up. In this example, the 3rd digit is 0 for easting and an 6 for northing. So if you used 6 digits in this example, they'd be 611 897 (rounding up). This means you find the intersection of gridlines 61 and 89. Then you go 100m further right, and 700m further up from this intersection. Since the map is scaled at 1:50,000 2mm on the map represents 100m. This point defines, and is the SW corner of, the 100m square 611 897 within gridsquare 61 89. Additional co-ordinate digits take you further NE from this point into this 100m square.

c. The 4th digits in each section specify the SW corner of the 10m square we're talking about within the 100m square 611 897 of gridsquare 61 89. In this case the co-ordinate reads 6106 east and 8965 north. This translates as 60m east of the 61 easting and 650m north of the 89 northing. In terms of CM, defining something to this level lets you place to spot accurately into one quadrant of a 20m x 20m terrain tile.

As another example, go back to Map 1 and find the feature located at Grid 633 859. No peeking at the answer, go to the map and try it out.

If you identified the jetty in Worser Bay, well done. If not, try again.

The Eastings and Northings referred to above reflect the direction of true North (and South), and East (and West). True North lines point in the direction of the North Pole, not Magnetic North, which is somewhere in eastern Canada (in Quebec?).

For the CMMC the distinction is meaningless - suffice it to say that north is up, south down, west to the left, and east to the right. If the CMMC overall campaign area is within 100km by 100km then no further system refinements are required.

Map 2: France (Box shows coverage of 100km x 100km Grid)

If the campaign area will encompass a greater area than this, then the 00 - 99 Easting and Northing lines will start to repeat. In most cases it will be obvious what is intended. For example if a Bn CO is at 97 89 and receives orders to move to 02 93, it is reasonable to expect that his orders are to move 6km in a north east direction, rather than 95km in a westerly direction! Especially if the orders combine some named objective ("move to the Reichswald in the vicinity Gr 02 93"), or a time limit ("move to Gr 02 93 within 30 mins"). Nevertheless, confusion could still be caused, and to alleviate this letters may be added to the start of a grid reference to indicate which 100km x 100km chunk of ground is being used. The following table shows which letter combinations are to be used for each area:

Table 1: Letter pattern for repeating 100km x 100km grid

This table can be extended to the right and upwards as required.

Exercises

Map 3: Lake Ferry Area (1:50,000 2cm = 1km) Click to Enlarge

Using Map 3:

Find the 4 figure grid for the following features:

1) Seagull Island
2) Lake Ferry

Find the 6 figure grid for the following features:

3) Fern Hill
4) White Stone Hill

Name the prominent feature at the following grids:

5) 86 82 / 87 82
6) 89 82
7) 852 807
8) 862 816

Map 4: Bocage Terrain (1:5,000 2cm = 100m) Click to Enlarge

Using Map 4:
Note: this map uses a section of a Combat Mission Map from the map editor. Each of the grids is 100m x 100m. Each of the small squares faintly visible on the map is a single terrain tile and measures 20m x 20m. Various friendly (Blue) and enemy (Red) positions are marked on the map.

Name the prominent feature at the following grids:

9) 0229 6295
10) 017 625

Find the 6 figure grid for the following features:

11) Friendly Section 2/A/III
12) Enemy Platoon (-)

Find the 8 figure grid for the following features:

13) Tank Corner
14) Enemy Panzer Sect.

Click here for answers to exercises