Graph and Data Skills

Data handling is a core geographical skill tested in every Edexcel B exam paper. You need to be able to draw graphs accurately, interpret what they show, calculate statistical measures, describe trends, and identify anomalies. These skills are worth a significant number of marks across all three papers, and they are skills you can improve dramatically with practice.

This lesson provides a comprehensive revision of the data skills you need, with worked examples and practice techniques for each one.

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Drawing Graphs

Bar Charts

Bar charts are the most commonly required graph in the exam. Follow these rules:

Rule	Why
Equal bar widths	Ensures visual fairness between categories
Equal gaps between bars	Distinguishes bars and improves readability
Y-axis starts at zero	Avoids exaggerating differences
Equal intervals on y-axis	Ensures accurate representation
Clear labels on both axes with units	Allows the reader to understand the data
A descriptive title	Tells the reader what the graph shows

Common exam instruction: "Using the data in Table 2, complete the bar chart on Figure 5." (3 marks)

How to score full marks:

1. Plot all bars accurately (1 mark per bar or group, depending on the question)
2. Ensure bars reach the correct height on the y-axis
3. Use a ruler for neat, straight bars

Line Graphs

Rule	Why
Plot points accurately	Incorrect plotting = incorrect answer
Connect points with straight lines (ruler)	Shows change clearly
Label axes with units	Enables interpretation
Use different line styles for multiple datasets	Distinguishes between lines

Scatter Graphs

Rule	Why
Plot each point using both x and y values	Shows the relationship between variables
Do NOT connect the points	Scatter graphs show correlation, not sequence
Draw a line of best fit if asked	Shows the general trend
Equal points above and below the line of best fit	Ensures the line represents the data fairly

Exam Tip: When completing a graph in the exam, use a sharp pencil and a ruler. Accuracy matters — if your bar is plotted at 45 when the correct value is 48, you will lose the mark. Take your time and double-check each plotted point against the data table.

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Interpreting Graphs

Describing Trends

Use this vocabulary to describe trends:

Trend	Language to Use
Increase	"Values rise from X to Y," "there is a steady/rapid increase"
Decrease	"Values fall from X to Y," "there is a gradual/sharp decline"
Fluctuation	"Values fluctuate between X and Y," "there is no clear trend"
Plateau	"Values level off at approximately X," "there is little change between..."
Peak	"Values reach a maximum of X in [month/location]"
Trough	"Values reach a minimum of X in [month/location]"
Anomaly	"Site C is an anomaly, showing a higher/lower value than the trend suggests"

Describing Correlations

Correlation	Description	Visual Pattern
Strong positive	As X increases, Y increases consistently	Points close to line rising left to right
Weak positive	General tendency for Y to increase with X, but scattered	Points loosely rising left to right
Strong negative	As X increases, Y decreases consistently	Points close to line falling left to right
Weak negative	General tendency for Y to decrease with X, but scattered	Points loosely falling left to right
No correlation	No clear relationship	Points scattered randomly

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Statistical Calculations

Mean

Mean = Sum of all values / Number of values

Example: Pedestrian counts at 5 sites: 45, 62, 38, 71, 54

Mean = (45 + 62 + 38 + 71 + 54) / 5 = 270 / 5 = 54 people

Median

1. Arrange in order: 38, 45, 54, 62, 71
2. Middle value = 54 (3rd of 5 values)

Mode

The most frequent value. If data is: 3, 4, 4, 5, 6, 7, 4, 8 → Mode = 4

Range

Range = Highest - Lowest

Range = 71 - 38 = 33 people

Interquartile Range (IQR)

Data (ordered): 12, 15, 18, 22, 25, 28, 31, 35, 38, 42, 45, 50

• Q1 (median of lower half): (18 + 22) / 2 = 20
• Q3 (median of upper half): (38 + 42) / 2 = 40
• IQR = 40 - 20 = 20

Percentage Calculations

Type	Formula	Example
Simple percentage	(Part / whole) × 100	25 shops out of 80 total = (25/80) × 100 = 31.25%
Percentage change	((New - old) / old) × 100	Population went from 50,000 to 65,000 = ((65000-50000)/50000) × 100 = 30% increase
Percentage of 360° (for pie charts)	(Percentage / 100) × 360	25% = (25/100) × 360 = 90°

Exam Tip: Always show your working for calculations. If you make an arithmetic error but your method is correct, you can still earn method marks. Writing just a final answer with no working risks losing all marks if it is wrong.

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Describing Trends in Detail

When describing trends, go beyond simple direction. The examiner wants detail:

The Four-Part Trend Description

1. Direction: "Values increase / decrease / fluctuate"
2. Magnitude: "from [start value] to [end value]"
3. Rate: "rapidly / gradually / steadily"
4. Variations: "with a slight dip at [point]" or "the rate of increase is steeper between [X] and [Y]"

Example: "River width increases steadily from 1.2m at Site 1 (1 km from the source) to 8.7m at Site 8 (8 km from the source). The rate of increase is relatively gradual between Sites 1 and 4 (1.2m to 3.1m over 3 km) but becomes much steeper between Sites 5 and 8 (3.8m to 8.7m over 3 km). Site 6 is a slight anomaly, showing a smaller width (5.2m) than the trend would suggest, possibly due to the channel being confined by rock outcrops at that location."

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Identifying Anomalies

An anomaly (or outlier) is a data point that does not fit the expected pattern. In the exam, you should:

1. Identify the anomaly clearly: "Site D is an anomaly"
2. Describe it: "showing a value of 45mm, which is higher than the downward trend would predict"
3. Suggest a reason (if asked): "This may be because a tributary joins the river upstream of Site D, introducing coarser sediment"

flowchart TD
    A["Identify the anomaly<br/>’Site D does not fit the trend’"] --> B["Describe it precisely<br/>’45mm vs expected ~35mm’"]
    B --> C["Explain possible cause<br/>’Tributary input of coarser sediment’"]
    C --> D["Consider if it affects conclusions<br/>’Overall trend still valid despite anomaly’"]

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Using Data to Support Arguments

In extended writing questions, data should be used as evidence to support geographical arguments:

Weak Use of Data

"Lots of people live in slums in Mumbai."

Strong Use of Data

"Over 60% of Mumbai's population — approximately 12 million people — live in informal settlements, with Dharavi alone housing over 1 million residents in an area of just 2.1 km²."

Integrating Data into Arguments

Technique	Example
Embed data in a sentence	"Discharge increases from 0.15 m³/s to 2.8 m³/s, an increase of over 1,700%"
Compare data points	"Site A has a footfall of 127, nearly six times higher than Site E at 23"
Use data to support causation	"The strong negative correlation (rs = -0.92) supports the hypothesis that pebble size decreases downstream"
Acknowledge uncertainty	"Although the correlation is strong (rs = -0.78), the sample size of only 8 means it should be interpreted with caution"

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Common Data Mistakes