Fieldwork Skills » Sphere of Influence Studies

What you'll learn this session

Study time: 30 minutes

What sphere of influence studies are and why they're important
How to design and conduct sphere of influence surveys
Methods for mapping and analysing sphere of influence data
How to interpret patterns in sphere of influence data
Real-world applications and case studies
Common challenges and how to overcome them

Introduction to Sphere of Influence Studies

Sphere of influence studies help us understand how far a settlement's services and facilities attract people from the surrounding area. This is crucial for understanding settlement hierarchies, planning new developments and making business decisions.

Key Definitions:

Sphere of influence: The area served by a settlement, from which people travel to use its services and facilities.
Settlement hierarchy: The ranking of settlements based on their size, importance and range of services.
Range: The maximum distance people are willing to travel to use a service.
Threshold population: The minimum number of customers needed for a service to be profitable.

🏠 Settlement Hierarchy

Settlements can be ranked from small hamlets to large cities. Each level offers different services with different ranges:

Hamlet: Few services, small sphere of influence
Village: Basic services (post office, pub)
Town: Medium range services (supermarkets, doctors)
City: High-order services (universities, specialist shops)

🗺 Factors Affecting Sphere of Influence

Several factors determine how far a settlement's influence extends:

Size and importance of the settlement
Range and quality of services offered
Transport links and accessibility
Competition from nearby settlements
Physical barriers like rivers or mountains

Designing Sphere of Influence Surveys

To study a settlement's sphere of influence, you need to collect data about where people come from to use services. Questionnaires are the most common method.

Creating Effective Questionnaires

Your questionnaire should include questions about:

Where respondents live (postcode or village/town name)
Purpose of their visit to the settlement
How often they visit
Mode of transport used
Alternative places they might visit for the same services

Sample Question Design

Good question: "Which town do you normally visit to do your weekly food shopping?" (Specific, clear)

Poor question: "Where do you shop?" (Too vague, unclear what type of shopping)

Sampling Strategies

To get reliable results, you need to think carefully about:

Sample size: Aim for at least 50 respondents, more if possible
Sampling locations: Choose busy areas like high streets, shopping centres, or car parks
Timing: Collect data on different days and times to capture different user groups
Stratified sampling: Try to include people of different ages, genders and backgrounds

📅 When to Survey

Weekdays capture commuters and regular shoppers. Weekends attract leisure visitors and families. Different times of day attract different demographics.

📍 Where to Survey

Choose multiple locations across the settlement to capture different types of visitors. Include main shopping areas, transport hubs and service centres.

👤 Who to Survey

Aim for a representative sample. Be aware of bias - e.g., surveying only during school hours will miss students and working parents.

Mapping and Analysing Sphere of Influence Data

Once you've collected your data, you need to process it to identify patterns and draw conclusions.

Creating Sphere of Influence Maps

There are several ways to visualise your data:

🗺 Delimiting Boundaries

Draw a line around the area from which most people (e.g., 90%) travel to use the settlement's services. This creates a boundary showing the settlement's sphere of influence.

📊 Isoline Maps

Draw lines connecting places with equal percentages of people visiting the settlement. For example, a 50% isoline connects all places where half the population visits your settlement.

Desire Lines

Desire lines show the movement of people from their homes to the settlement. The thickness of the line can represent the number of people making that journey.

To create a desire line map:

Plot the location of your settlement in the centre of your map
Plot the locations of surrounding settlements
Draw lines connecting each surrounding settlement to your central settlement
Vary the thickness of each line based on the number of visitors from that location

Case Study Focus: Market Town Sphere of Influence

A study of Marlborough, Wiltshire, showed how a traditional market town's sphere of influence has changed over time. In the 1950s, most visitors came from within 10km. By 2010, improved roads meant visitors regularly travelled up to 25km, but competition from larger towns like Swindon had reduced Marlborough's influence to the north.

The study used questionnaires at the weekly market and in the high street shops. Desire lines showed strong connections with smaller villages but weaker connections with areas near competing towns.

Interpreting Patterns

When analysing your sphere of influence data, look for these patterns:

Distance decay: The number of visitors typically decreases as distance from the settlement increases
Breaking points: Areas where the influence of two competing settlements is equal
Transport corridors: The sphere of influence often extends further along major transport routes
Physical barriers: Rivers, hills, or poor road connections can create sharp boundaries in the sphere of influence

Comparing Different Services

Different services have different spheres of influence:

🍱 Low-Order Services

Convenience stores, primary schools, post offices. Small sphere of influence (1-3km). People need these frequently and won't travel far.

🏪 Medium-Order Services

Supermarkets, secondary schools, doctors. Medium sphere of influence (5-10km). People visit weekly or monthly.

🏢 High-Order Services

Specialist shops, hospitals, theatres. Large sphere of influence (20km+). People travel further for these occasional needs.

Common Challenges and Solutions

Sphere of influence studies can be tricky. Here are some common problems and how to solve them:

⚠ Challenges

People may not want to stop and answer questions
Weather can affect data collection
Responses might not be accurate or truthful
Online shopping is changing traditional patterns
Sample might not be representative

💡 Solutions

Keep questionnaires short and simple
Have a backup indoor location for bad weather
Cross-check responses with observation data
Include questions about online shopping habits
Use stratified sampling techniques

Modern Approaches

Technology is changing how we study spheres of influence:

Mobile phone data: Shows movement patterns without needing surveys
Social media check-ins: Reveal popular destinations
GIS mapping: Allows complex analysis of patterns
Online questionnaires: Can reach more people than street surveys

Exam Tip

In your exam, you might be asked to:

Design a sphere of influence study
Interpret sphere of influence maps
Explain factors affecting a settlement's sphere of influence
Compare the spheres of influence of different services

Always link your answers to geographical theories like central place theory and consider how changes in transport and technology affect spheres of influence.

🧠 Test Your Knowledge!