Welcome to Map Skills: Grid References!
Have you ever tried to find a hidden treasure or tell a friend the exact spot where you are meeting in a huge park? Maps are fantastic tools for exploring our world, but to find exact places on them, we need a special code. That code is called a grid reference!
In this chapter, we will learn how to read and use both four-figure and six-figure grid references using Ordnance Survey (OS) maps. Don't worry if this seems tricky at first—once you learn the secret rule, you will be finding locations like a professional explorer!
1. Understanding Map Grid Lines
When you look closely at an Ordnance Survey map, you will see a criss-cross pattern of blue lines. This creates a grid of squares all over the map. Each standard square on a local map represents an area of \(1\text{ km} \times 1\text{ km}\) (\(1\text{ km}^2\)).
Meet the Lines: Eastings and Northings
There are two types of grid lines on a map:
1. Eastings (Vertical Lines):
These are the lines that go straight up and down. They have numbers along the top and bottom edges of the map. As you move from left to right (towards the east), the numbers get bigger!
2. Northings (Horizontal Lines):
These are the lines that go straight across from left to right. They have numbers along the left and right sides of the map. As you move from the bottom to the top (towards the north), the numbers get bigger!
Did You Know?
The Ordnance Survey divides the whole of Great Britain into large squares measuring \(100\text{ km} \times 100\text{ km}\). Each of these huge squares has a two-letter name, such as TQ, SK, or NY!
2. The Golden Rule of Grid References
There is one super-important rule that you must always remember when reading grid references:
Always quote the Eastings first, then the Northings!
Memory Tricks to Help You Remember:
Here are two easy ways to keep the order straight:
• "Along the corridor, then up the stairs!" (Walk along the hallway first using Eastings, then climb up the stairs using Northings.)
• "X before Y" or "E before N" (Just like in the alphabet, Eastings comes before Northings!)
Key Takeaway:
Always go across (left to right) before you go up (bottom to top)!
3. Four-Figure Grid References
A four-figure grid reference is used to identify an entire \(1\text{ km} \times 1\text{ km}\) grid square on a map.
How It Works:
A four-figure reference has 4 numbers:
• The first 2 digits tell you the Easting line on the left-hand side of the square.
• The last 2 digits tell you the Northing line on the bottom of the square.
Step-by-Step: How to Find a Four-Figure Grid Reference
Step 1: Find the square on the map that contains the feature you want to locate.
Step 2: Put your finger on the bottom-left corner of that square.
Step 3: Look along the bottom or top of the map to find the number of the vertical line directly to the left of your finger (the Easting). Let's say it is 32.
Step 4: Look at the side of the map to find the number of the horizontal line directly below your finger (the Northing). Let's say it is 26.
Step 5: Put the two numbers together: 3226. That is your four-figure grid reference!
Key Takeaway:
Always look at the bottom-left corner of the square. Read the vertical line first, then the horizontal line.
4. Six-Figure Grid References
What if you want to pinpoint a tiny, specific object inside a grid square, like a church tower, a bridge, or a campsite? A whole grid square is large, so a four-figure reference is not exact enough.
This is where a six-figure grid reference comes in! It pinpoints a location with an accuracy of \(100\text{ metres} \times 100\text{ metres}\).
How It Works:
A six-figure reference splits the four-figure reference into two halves of 3 digits each: EEE NNN.
• Digits 1 and 2: The Easting line on the left side of the square.
• Digit 3: How many tenths (from 0 to 9) to count across the square towards the right.
• Digits 4 and 5: The Northing line at the bottom of the square.
• Digit 6: How many tenths (from 0 to 9) to count up the square towards the top.
Step-by-Step: How to Find a Six-Figure Grid Reference
Imagine there is a windmill inside grid square 3226:
Step 1: Start at the left line of your square (Easting 32).
Step 2: Imagine dividing the bottom of the square into 10 equal mini-steps from 0 to 9. Count how many tenths across the windmill is. If it is 4 tenths across, your first three digits are 324.
Step 3: Now look at the bottom line of your square (Northing 26).
Step 4: Imagine dividing the side of the square into 10 equal mini-steps from 0 to 9. Count how many tenths up the windmill is. If it is 7 tenths up, your last three digits are 267.
Step 5: Put both parts together to get your six-figure reference: 324267!
Key Takeaway:
A six-figure reference gives an exact spot by breaking each square down into tenths: [Easting][tenths across] [Northing][tenths up].
5. Common Mistakes to Avoid
Even the best geographers can make simple slips. Keep an eye out for these common traps:
• Mixing up the order: Never read the Northing (up) before the Easting (across). Remember: along the corridor, then up the stairs!
• Looking at the wrong corner: When finding a four-figure reference, always check the bottom-left corner of the square, not the top or right edges.
• Squashing numbers in the wrong place: Do not write a four-figure reference and stick two extra numbers on the very end (like writing 322647). The tenths must go right next to their matching line numbers (324267).
• Counting backwards: Always count your tenths from left to right and from bottom to top.
• Forgetting zero: If a feature sits directly on the left grid line or the bottom grid line, its tenth value is 0, not 1 or 10!
Quick Review Summary
• Eastings: Vertical grid lines numbered from left to right (moving east).
• Northings: Horizontal grid lines numbered from bottom to top (moving north).
• Rule: Eastings first, Northings second (Along the corridor, then up the stairs).
• 4-Figure References: Locates a \(1\text{ km} \times 1\text{ km}\) square using the bottom-left corner (e.g., 3226).
• 6-Figure References: Pinpoints a specific feature to within \(100\text{ metres}\) by adding tenths across and tenths up (e.g., 324267).