Have you ever tried to meet a friend in a huge, crowded park without a specific landmark? Ordnance Survey (OS) maps solve this problem using a precise coordinate system of blue grid lines. The vertical lines are called because their numbers increase as you move eastwards (left to right). The horizontal lines are , increasing upwards towards the north (bottom to top).
A is the box formed by these intersecting lines, representing exactly of real-world land, regardless of the map . When identifying a specific square, you always read the easting first, followed by the northing. A helpful rule to remember is "along the corridor, then up the stairs".
A directs you to a specific square by pointing to its . For example, to find square 2461, you find vertical line 24 and horizontal line 61, and look at the square to the top-right of that intersection.
A provides pinpoint accuracy to within . These are constructed by mentally dividing the into ten smaller sections (tenths) across and upwards. A 6-figure reference consists of two 3-digit numbers:
Worked Example:
Find the for a church spire located in 1751.
Step 1: Identify the 4-figure square (1751).
Step 2: Estimate tenths across from Easting line 17. If the spire is 4 tenths across, the first half is 174.
Step 3: Estimate tenths up from Northing line 51. If the spire is 6 tenths up, the second half is 516.
Step 4: Combine the digits. The final reference is 174516.
A map the exact size of the real world would be impossible to fold and carry. shrinks the real world down to fit on a page, representing the ratio between map distance and actual distance.
A displays this mathematically, such as 1:50,000, meaning one unit on the map equals 50,000 of the same units in reality. OS maps typically come in 1:25,000 (where ), or 1:50,000 (where ).
You can also calculate distances using a (written out in words) or by physically measuring with a (a graduated visual bar at the bottom of the map).
Worked Example:
How far apart in the real world are two campsites that measure 14 cm apart on a map with a of "two centimetres to one kilometre"?
Step 1: Identify the factor.
Step 2: Divide the measured map distance by the factor.
Step 3: State the final answer with units.
Worked Example:
Find the straight-line distance between a church and a post office using a where each large division is 1 km and each small subdivision is 100 m.
Step 1: Place a straight edge of scrap paper between the church and the post office on the map, marking the exact center of each symbol.
Step 2: Move the paper to the bar at the bottom of the page.
Step 3: Align your first mark exactly with the '0' line on the .
Step 4: Read the distance at the second mark.
Looking at a completely flat map, it can be difficult to picture towering hills or deep river channels. Maps represent physical using several techniques, most importantly through a specific type of isoline called a .
are lines drawn on a map that connect points of equal value. A key rule is that must never touch or cross each other. For example, isobars show equal atmospheric pressure, while connect points of equal height above mean sea level.
The height difference between each successive is the , typically or . Spotting patterns in these lines reveals the landscape:
Specific heights are also marked using a (a black dot with a number) or a (a blue triangle showing a surveyed peak).
You can identify specific landforms using the "V rule". A is formed when contours create a V-shape pointing uphill towards higher numbers. Conversely, a forms when the V-shape points downhill towards lower numbers.
Knowing the exact steepness of a hill is crucial for anyone planning a cycling route or laying a new railway line. is a mathematical ratio that expresses this steepness, often thought of as "rise over run".
To calculate it, you need the height difference () and the real-world map distance, known as the . Both values must be converted into the exact same unit (usually metres) before dividing.
Worked Example: Calculating
Calculate the between a farm at 120 m and a forest at 370 m. The map distance between them is 5 cm on a 1:50,000 map.
Step 1: Calculate the .
Step 2: Calculate the using the map .
Step 3: Apply the formula.
Step 4: State the final answer as a ratio.
Students frequently swap eastings and northings when writing 4-figure or 6-figure references. Always remember 'along the corridor (eastings) and up the stairs (northings)' to ensure you read the horizontal axis first.
In gradient calculation questions, marks are often dropped because students forget to convert the map distance into real-world metres (Horizontal Equivalent) before dividing. Both the VI and HE must be in identical units.
When describing contour patterns in an exam (such as identifying landforms in Paper 1), avoid using vague terms like 'left' or 'above'; examiners expect you to use specific compass directions (North, South, East, West) and exact grid references.
For 6-figure grid references, OCR mark schemes typically allow a small tolerance of +/- 1 for the 3rd and 6th digits, so do not panic if your visual estimation of the 'tenths' is not millimeter-perfect.
Eastings
Vertical grid lines on an Ordnance Survey map that increase in numerical value as you move eastwards.
Northings
Horizontal grid lines on an Ordnance Survey map that increase in numerical value as you move northwards.
Grid Square
The box formed by intersecting grid lines, representing exactly () of real-world land.
4-Figure Grid Reference
A four-digit coordinate that identifies a specific grid square.
Bottom-Left Corner
The intersection of the easting and northing lines used to name a grid square; always the reference point for a 4-figure coordinate.
6-Figure Grid Reference
A six-digit coordinate providing pinpoint accuracy to within by dividing a grid square into tenths.
Scale
The mathematical ratio between a distance measured on a map and the actual distance on the ground.
Ratio Scale
A scale expressed as a ratio (e.g. 1:50,000) where one unit on the map equals a specified number of units in reality.
Statement Scale
A scale expressed in words, such as "two centimetres to one kilometre".
Linear Scale
A graduated scale bar at the bottom of a map used for direct measurement using a straight edge or string.
Relief
The physical height, shape, and slope of the land surface, including features like hills and valleys.
Isolines
Lines drawn on a map that connect points of equal value, such as height (contours) or pressure (isobars).
Contour Line
An isoline drawn on a map connecting points of equal height above mean sea level.
Vertical Interval (VI)
The difference in vertical height between two successive contour lines on a map.
Spot Height
A black dot with a number showing the exact surveyed height of the land at that specific point.
Trigonometrical (Trig) Station
A small blue triangle marking the height of a concrete survey pillar used for mapping.
Valley
A low area of land between hills, identified by V-shaped contours pointing uphill towards higher land.
Spur
A piece of high ground sticking out from a hill, identified by V-shaped contours pointing downhill towards lower land.
Gradient
A measure of the steepness of a slope, usually expressed as a ratio between the vertical rise and horizontal distance.
Horizontal Equivalent (HE)
The actual real-world horizontal distance between two points, calculated using the map scale.
Put your knowledge into practice — try past paper questions for Geography B
Eastings
Vertical grid lines on an Ordnance Survey map that increase in numerical value as you move eastwards.
Northings
Horizontal grid lines on an Ordnance Survey map that increase in numerical value as you move northwards.
Grid Square
The box formed by intersecting grid lines, representing exactly () of real-world land.
4-Figure Grid Reference
A four-digit coordinate that identifies a specific grid square.
Bottom-Left Corner
The intersection of the easting and northing lines used to name a grid square; always the reference point for a 4-figure coordinate.
6-Figure Grid Reference
A six-digit coordinate providing pinpoint accuracy to within by dividing a grid square into tenths.
Scale
The mathematical ratio between a distance measured on a map and the actual distance on the ground.
Ratio Scale
A scale expressed as a ratio (e.g. 1:50,000) where one unit on the map equals a specified number of units in reality.
Statement Scale
A scale expressed in words, such as "two centimetres to one kilometre".
Linear Scale
A graduated scale bar at the bottom of a map used for direct measurement using a straight edge or string.
Relief
The physical height, shape, and slope of the land surface, including features like hills and valleys.
Isolines
Lines drawn on a map that connect points of equal value, such as height (contours) or pressure (isobars).
Contour Line
An isoline drawn on a map connecting points of equal height above mean sea level.
Vertical Interval (VI)
The difference in vertical height between two successive contour lines on a map.
Spot Height
A black dot with a number showing the exact surveyed height of the land at that specific point.
Trigonometrical (Trig) Station
A small blue triangle marking the height of a concrete survey pillar used for mapping.
Valley
A low area of land between hills, identified by V-shaped contours pointing uphill towards higher land.
Spur
A piece of high ground sticking out from a hill, identified by V-shaped contours pointing downhill towards lower land.
Gradient
A measure of the steepness of a slope, usually expressed as a ratio between the vertical rise and horizontal distance.
Horizontal Equivalent (HE)
The actual real-world horizontal distance between two points, calculated using the map scale.