OS Map Skills

Ordnance Survey (OS) maps are one of the most important tools in geography. They are used extensively in fieldwork planning, data collection and analysis, and they feature prominently in the Edexcel B exam. This lesson covers all the OS map skills you need to master: grid references, scale, distance, contour lines, relief, cross-sections and feature identification.

OS map questions appear in every GCSE Geography exam paper. They are worth practising because they offer guaranteed marks — unlike essay questions where opinions may vary, map skills questions have definite correct answers.

---

Grid References

4-Figure Grid References

A 4-figure grid reference identifies a 1 km x 1 km grid square on the map. It is accurate enough to locate a general area but not a precise point.

How to read a 4-figure grid reference:

1. Read along the bottom of the map (the easting) to find the vertical grid line on the left side of the square — this gives the first two digits
2. Read up the side of the map (the northing) to find the horizontal grid line at the bottom of the square — this gives the last two digits
3. Always go along the corridor and up the stairs (eastings first, then northings)

Example: If the grid square has easting 34 on its left edge and northing 56 on its bottom edge, the 4-figure grid reference is 3456.

6-Figure Grid References

A 6-figure grid reference identifies a point within a grid square to the nearest 100 metres, making it much more precise.

How to read a 6-figure grid reference:

1. Read the 4-figure grid reference as above (e.g. 34, 56)
2. Mentally divide the grid square into 10 equal parts both horizontally and vertically
3. Estimate how many tenths across the square the point is — this becomes the 3rd digit (e.g. if it is 7/10 across, the easting becomes 347)
4. Estimate how many tenths up the square the point is — this becomes the 6th digit (e.g. if it is 3/10 up, the northing becomes 563)
5. The 6-figure grid reference is 347563

Reference Type	Accuracy	Format	Example
4-figure	1 km²	EENN	3456
6-figure	100 m²	EEENNN	345563

Exam Tip: The most common mistake with grid references is getting eastings and northings the wrong way round. Remember: along the corridor (eastings) before up the stairs (northings). Or: the letter E comes before N in the alphabet — Eastings before Northings.

---

Scale and Distance

Understanding Map Scale

OS maps come in two main scales:

Scale	Map Name	Detail Level	1 cm on map =
1:25,000	Explorer	High detail (paths, field boundaries, individual buildings)	250 m on the ground
1:50,000	Landranger	Medium detail (roads, settlements, major features)	500 m on the ground

Measuring Straight-Line Distance

1. Place the edge of a piece of paper between the two points on the map
2. Mark both points on the paper edge
3. Place the paper along the map's scale bar
4. Read off the distance

Or calculate mathematically:

1. Measure the distance on the map in centimetres using a ruler
2. Multiply by the scale factor

Map Scale	Distance on map (cm)	Distance on ground
1:25,000	4 cm	4 x 250 = 1,000 m = 1 km
1:50,000	4 cm	4 x 500 = 2,000 m = 2 km
1:25,000	6 cm	6 x 250 = 1,500 m = 1.5 km
1:50,000	3 cm	3 x 500 = 1,500 m = 1.5 km

Measuring Winding Distances

For curved features like rivers or roads:

1. Place a piece of string along the route, following every curve
2. Straighten the string and measure it against the scale bar
3. Alternatively: Use the edge of paper, making small marks and rotating the paper around each bend

Exam Tip: When measuring winding distances, take your time and follow the route carefully. If the question asks for the distance along a road, follow the road exactly — do not cut corners. A piece of string is the most accurate method, but the paper-edge technique works well with practice.

---

Contour Lines and Relief

What Are Contour Lines?

Contour lines are brown lines on an OS map that connect points of equal height above sea level. They show the shape and gradient of the land (the relief).

Reading Contour Lines

Contour Pattern	What It Shows
Lines close together	Steep gradient — the height changes rapidly over a short distance
Lines far apart	Gentle gradient — the height changes slowly over a longer distance
Lines forming a V pointing uphill	A valley — the V always points upstream
Lines forming a V pointing downhill	A spur — a ridge of high ground extending from a hill
Concentric circles	A hilltop or summit — the highest point is inside the smallest circle
Concentric circles with hatching	A depression or hollow — hatching marks point inwards
Evenly spaced lines	A uniform slope — constant gradient

Contour Intervals

Map Scale	Contour Interval
1:25,000 (Explorer)	5 metres (with index contours every 25 metres in bold)
1:50,000 (Landranger)	10 metres (with index contours every 50 metres in bold)