Map Grid Reference (MGR)

A map grid reference number (MGR for short) is a position on a map. Is uses both an Eastings (North to South grid line) and Northings (East to West grid lines) value to specify a point. Look at the examples below to see how this is done.

 

4 Digit MGR

The four digit MGR is the most broad form of giving a direction. In a 1:50000 map, a single square covers the area of 1 kilometer square. This makes referencing points on the map rather vague and is only good for giving a general guide to the area a person maybe in.

In the picture, here is how you would find out the four digit MGR of the HQ building (the one in gray). First you would find how far East it is. The number corresponding is 21. You would next find out how far North it is. The number it falls in is 11. So combining these two numbers, you get 21-11 or 2111, which is the four digit MGR.

*The numbers taken are always from the smaller number, or the number that the grid 'starts' from. 
 

6 Digit MGR

The six digit MGR brings accuracy to a location. Instead of giving a 1 x 1 km grid, you now have a point that is 100m x 100m, making your location far more accurate and hence more useful. Combined with a clue

(for example a temple in that MGR location), finding places is quite possible.

The 6 digit MGR follows the 4 digit MGR in the form that you read it. The only difference is now the 3rd and 6th digit are more specific. In this example of the HQ building. You can see that when sub-divided, more specific location is 216111.

 

8 Digit MGR

Using a compass or ruler, it is actually possible to further narrow down the location of a point even further.

In a 1:50000 map, a single grid measures 2cm by 2cm. When divided into 10 parts (as for the 6 digit MGR) you get a 2mm by 2mm grid. The smallest scale on your ruler or compass is 1mm. What this means is that the last digit in the eight digit MGR will either be a 5 (to represent the points in between the 2mm intervals) and when the point is inline with these intervals, the last digit will be 0. Hence the last digit can only either be a 5 or a 0. 

In the example given, you have the located halfway between the Eastings 216 and 217. However the point is nicely inline with the 111 Northing line. Hence the eight digit MGR is 21651110.

Tips:

Remembering which value to come first is sometimes confusing. Just remember in your own way that the reading on how far EAST comes before how far NORTH. A simple phase to remember is "To reach a MGR, first go right than up." Sometimes large objects do not fit nicely inside grids. How do we label these accurately? If it is a really huge location, you could either pick a point (eg. the stadium gate) and give the MGR of that specific location or if you need to label the entire location, find the most central and give the MGR reading of that

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