Four- and Six-Figure Grid References

Understanding Grid References

Ordnance Survey (OS) maps use a grid of vertical and horizontal lines called grid lines. These lines divide the map into squares, making it easier to locate places precisely. The vertical lines are called eastings because they measure eastwards, and the horizontal lines are called northings because they measure northwards.

A grid reference is a set of numbers that tells you exactly where a feature is on the map by using these eastings and northings. It helps you pinpoint locations quickly and accurately, which is essential for navigation and map reading.

There are two common types of grid references used at GCSE level:

• Four-figure grid references 6 locate a feature within a 1 km by 1 km square on the map.
• Six-figure grid references 6 locate a feature more precisely within a 100 m by 100 m square.

Four-Figure Grid References

A four-figure grid reference identifies the grid square in which a feature is found. It uses the numbers on the eastings (vertical lines) and northings (horizontal lines) to give the bottom-left corner of the square.

To read a four-figure grid reference:

1. Find the easting number on the bottom or top of the map that is just to the left of the feature.
2. Find the northing number on the side of the map that is just below the feature.
3. Write the easting first, then the northing, each as two digits (e.g. 45 62).

This tells you the 1 km square where the feature lies, but not the exact spot inside it.

For instance, if a feature lies in the square with eastings 45 and northings 62, the four-figure grid reference is 4562.

Four-figure references are useful for general locations but not for precise points.

For example, if a village is located in the square bounded by eastings 32 and 33, and northings 47 and 48, its four-figure grid reference is 3247.

Six-Figure Grid References

Six-figure grid references give a much more precise location by dividing each 1 km square into 100 smaller squares, each 100 m by 100 m.

To find a six-figure grid reference:

1. Start with the two-digit easting of the 1 km square (the vertical grid line to the left).
2. Estimate how many tenths (0 to 9) of the square the feature is across from the left side. This gives the third digit of the easting.
3. Do the same for the northing: start with the two-digit northing of the 1 km square (the horizontal grid line below).
4. Estimate how many tenths (0 to 9) of the square the feature is up from the bottom. This gives the third digit of the northing.
5. Combine these to form a six-digit number: three digits for eastings, then three digits for northings.

This locates the feature to within 100 metres on the map.

For example, if a feature is 4 tenths across and 7 tenths up within the square with eastings 45 and northings 62, the six-figure grid reference is 454627.

Practical Application

Grid references are used to find and describe locations on OS maps, such as towns, rivers, hills, or roads. They are essential for navigation, fieldwork, and understanding map data.

When interpreting grid references:

• Always read the easting first (left to right), then the northing (bottom to top).
• Check carefully that you have the correct digits and order.
• Remember that four-figure references give a square of 1 km by 1 km, while six-figure references give a more exact point within that square.

For example, if a feature lies 6 tenths across and 3 tenths up inside the square bounded by eastings 53 and 54, and northings 21 and 22, the six-figure grid reference is 536213. This means you start with the easting 53, add 6 tenths to get 536, then start with the northing 21 and add 3 tenths to get 213.

For example, when using a six-figure grid reference, imagine the 1 km square as a 10 by 10 grid. Count how many small squares across and up the feature lies.

Common mistakes include:

• Mixing up eastings and northings.
• Using the wrong number of digits.
• Not estimating tenths correctly for six-figure references.

Always practise with real OS maps to improve accuracy.

For instance, if you want to locate a church on an OS map, first find the 1 km square using a four-figure reference, then refine the location with a six-figure reference for better precision.