Map Symbols and Contour Lines Explained for KS3 Geography

Map symbols are standardised pictures and colours that represent real-world features on Ordnance Survey (OS) maps, while contour lines are brown lines connecting points of equal height above sea level. Together they allow a reader to visualise the physical landscape — hills, valleys, cliffs and gradients — from a flat sheet of paper.

What are map symbols on an OS map?

Ordnance Survey maps use a consistent system of symbols to show both physical features (natural landscape) and human features (built environment). Every OS map includes a key that explains what each symbol means, but knowing the most common symbols without needing to check the key saves time in assessments and fieldwork.

Common physical feature symbols

Symbol | Feature
Blue lines (thin) | Rivers and streams
Blue lines (wider/shading) | Lakes and reservoirs
Green shading | Woodland and forests
Dotted brown lines | Footpaths and bridleways
Black dotted lines | Boundaries (county, parish)

Common human feature symbols

Symbol | Feature
Red lines (thick) | A-roads (primary roads)
Yellow lines | B-roads (secondary roads)
Black lines (thin) | Lanes and minor roads
Blue squares/rectangles | Buildings (general)
Cross (+) | Church with a tower
Circle with dot | Spot height (exact elevation in metres)
Blue P | Car park
Blue triangle (solid) | Youth hostel

The Ordnance Survey publishes its full symbol key for all map scales on its website, and it is worth bookmarking this for KS3 and GCSE geography work.

What are contour lines and what do they show?

A contour line connects all points at the same height (altitude) above sea level. On Ordnance Survey 1:50,000 Landranger maps — the most commonly used scale at KS3 — contour lines are drawn at 10-metre intervals, meaning each line represents a height 10 metres above or below the adjacent lines.

Key principle: contour lines never cross, because no single point on the ground can be at two different heights simultaneously.

How to read contour lines

1. The number on the line tells you the height in metres above sea level. On most OS maps, every fifth contour (at 50-metre intervals) is printed slightly thicker and labelled with the height. The numbers always read with the top of the number pointing uphill.

2. Spacing shows gradient:

Contour spacing | What it means | Typical landscape
Far apart (wide gaps) | Gentle gradient | Lowland plain, gentle hillside
Close together | Steep gradient | Hillside, escarpment
Very close together | Very steep | Cliff or near-vertical slope

3. Shape shows landform:

Contour pattern | Landform
Concentric circles, increasing inward | Hill or mountain
V-shape pointing uphill (upstream) | Valley (the V always points upstream)
V-shape pointing downhill | Ridge or spur
Contours close, then spreading | Cliff at the top, gentler below

Worked example: reading a cross-section

A cross-section is a diagram showing what the land would look like if you cut through it vertically, like a slice through a cake. KS3 geography assessments often ask students to sketch a cross-section from a map extract.

Method:

Place the edge of a piece of paper along the line of your cross-section.

Mark every point where a contour line crosses the edge of the paper, writing the height value next to each mark.

Transfer these marks onto graph paper, plotting height on the y-axis and distance on the x-axis.

Join the dots with a smooth curve.

Example heights along a 2 km cross-section:

Distance from A (m) | Height (m)
0 | 80
400 | 100
700 | 140
1000 | 160 (hilltop)
1400 | 120
2000 | 60

The resulting curve shows a hill with a steeper eastern approach (contours close together from 400–700 m) and a gentler western descent.

Map scale and what it means for reading symbols

OS maps are published at different scales, each suited to different purposes.

Scale | Name | Best use
1:25,000 | Explorer (orange) | Walking, detailed fieldwork, shows fields and footpaths
1:50,000 | Landranger (pink) | Overview of an area, most common in KS3 assessments
1:250,000 | Road map | Route planning, does not show contours or footpaths

On a 1:50,000 map, 1 cm on the map = 500 m on the ground (2 cm = 1 km). On a 1:25,000 map, 1 cm = 250 m (4 cm = 1 km).

Grid squares on a 1:50,000 Landranger map each measure 2 cm × 2 cm, representing 1 km × 1 km on the ground. This makes distance estimation quick: count the grid squares a route crosses and each one adds 1 km to the total.

Why map reading matters in geography

The DfE's KS3 geography curriculum requires students to interpret Ordnance Survey maps and to use fieldwork and geographical skills to describe and analyse physical and human processes. Map skills — including reading symbols, interpreting contours, calculating grid references and measuring distance — underpin both classroom assessments and fieldwork in Year 7, Year 8 and Year 9.

Being able to read a map fluently is also a practical life skill. The Ordnance Survey has mapped Great Britain continuously since 1791, producing the most detailed topographic coverage of any country. Its maps are used by planners, emergency services, environmental scientists and hikers — and the skills to read them are transferable across all of these contexts.

Frequently asked questions

What do contour lines close together mean?

Contour lines that are close together indicate a steep slope — the land is changing height rapidly over a short horizontal distance. Lines very close together (almost touching) suggest a cliff or near-vertical face. Lines far apart indicate a gentle gradient. The rule is: the closer the lines, the steeper the slope.

How do I tell if a river is flowing uphill or downhill on an OS map?

Rivers always flow downhill, from high contours to low ones. On an OS map, the V-shapes formed by contour lines crossing a valley always point upstream (uphill). The river flows in the opposite direction — toward the open end of the V and toward lower ground. Blue arrows on some maps also show flow direction directly.

What is the difference between a 1:25,000 and a 1:50,000 OS map?

Scale refers to the ratio between map distance and real-world distance. On a 1:25,000 (Explorer) map, 1 cm represents 250 m on the ground — it shows more detail, including individual field boundaries and footpaths. On a 1:50,000 (Landranger) map, 1 cm represents 500 m — it covers a wider area but shows less fine detail. Most KS3 assessments use 1:50,000 maps; fieldwork often uses 1:25,000.

How do I find the height of a hill from a contour map?

Locate the summit (the centre of the innermost contour ring). The height label on the nearest labelled contour tells you a baseline. Count the unlabelled contour lines between the labelled line and the summit, multiplying by the contour interval (10 m on Landranger maps). If a spot height (a small dot with a number in metres) sits at the summit, use that — it is the most precise measurement available.

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