Bruce September 19, 2025 GIS, Data

UK Census 2021 Data GIS Mapping Tutorial

Introduction

The UK Census 2021 represents the most comprehensive snapshot of the UK population in a decade, providing invaluable demographic, social, and economic data. This tutorial will guide you through the process of accessing, processing, and visualizing Census 2021 data using Geographic Information Systems (GIS), enabling you to create compelling maps and conduct spatial analysis.

Understanding UK Census 2021 Data Structure

Geographic Hierarchy

The UK Census 2021 data is organized in a hierarchical geographic structure:

Output Areas (OAs): The smallest geographic units, typically containing 40-125 households
Lower Super Output Areas (LSOAs): Groups of OAs with populations of 400-1,200 households
Middle Super Output Areas (MSOAs): Collections of LSOAs with 2,000-6,000 households
Local Authority Districts (LADs): Administrative boundaries
Counties and Regions: Higher-level administrative areas

Data Categories

The Census 2021 covers numerous topics including:

Population and household composition
Age and sex demographics
Ethnicity and country of birth
Religion and language
Health and disability
Housing characteristics
Employment and occupation
Education qualifications
Travel to work patterns

Data Sources and Access Points

Official Data Portals

ONS (Office for National Statistics)

Main repository: https://www.ons.gov.uk/census
Bulk downloads available for statistical data
Boundary data through ONS Geography portal

NOMIS

User-friendly interface for data queries
Custom table creation capabilities
API access for automated downloads

UK Data Service

Academic access to detailed datasets
Safeguarded and secure data options
Teaching datasets for educational use

Boundary Data Sources

ONS Open Geography Portal

Generalised and full resolution boundaries
Various formats: Shapefile, GeoJSON, KML
Consistent coding systems across geographies

Essential GIS Software Options

Desktop GIS Solutions

QGIS (Recommended for beginners)

Free and open-source
Excellent Census data plugins
Strong community support
Cross-platform compatibility

ArcGIS Pro

Industry standard
Advanced analytical capabilities
Requires licensing
Integrated with Esri ecosystem

MapInfo Pro

Strong for business applications
Excellent data handling
Commercial license required

Web-based Solutions

ArcGIS Online

Cloud-based mapping platform
Easy sharing capabilities
Subscription-based pricing

Carto

Web-based visualization platform
Good for interactive maps
Freemium model available

Step-by-Step Tutorial: Creating Your First Census Map

Step 1: Data Acquisition

Download Census Data:

Visit the ONS Census 2021 bulk downloads page
Select your geography level (recommend starting with MSOA)
Choose your topic (e.g., “Age by single year”)
Download the CSV file

Download Boundary Data:

Access ONS Open Geography Portal
Navigate to Census 2021 boundaries
Select matching geography (MSOA boundaries)
Download in Shapefile format

Step 2: Setting Up QGIS

Initial Setup:

Install QGIS (latest LTR version recommended)
Install QuickOSM plugin for background mapping
Set project CRS to British National Grid (EPSG:27700)

Loading Boundary Data:

Drag shapefile into QGIS
Right-click layer → Properties → Symbology
Set to “No fill” with black outline for initial viewing

Step 3: Data Preparation

Cleaning Census Data:

Common data preparation steps:
- Remove unnecessary columns
- Handle missing values (often coded as -1 or -2)
- Create derived variables (percentages, ratios)
- Ensure geographic codes match boundary data

Key Fields to Retain:

Geography code (e.g., MSOA21CD)
Geography name
Your variables of interest
Total population (for percentage calculations)

Step 4: Joining Data to Boundaries

In QGIS:

Right-click boundary layer → Properties → Joins
Add new join
Join field: Geography code in boundary layer
Target field: Geography code in CSV
Select fields to join
Apply and OK

Step 5: Creating Choropleth Maps

Symbolizing Data:

Layer Properties → Symbology
Change from “Single Symbol” to “Graduated”
Select your variable of interest
Choose classification method:
- Quantiles: Equal numbers in each class
- Natural Breaks: Optimizes class boundaries
- Equal Interval: Equal-sized class ranges

Color Scheme Selection:

Use ColorBrewer palettes for accessibility
Sequential schemes for continuous data
Diverging schemes for data with natural midpoint
Avoid red-green combinations (colorblind accessibility)

Step 6: Map Composition and Layout

Essential Elements:

Clear, descriptive title
Legend with meaningful class labels
Scale bar
North arrow
Data source attribution
Date of data collection

Layout Tips:

Use consistent fonts (Arial or Helvetica recommended)
Ensure sufficient contrast between text and background
Leave white space for readability
Consider your audience and purpose

Advanced Techniques

Multi-Variable Analysis

Creating Composite Indices:

sql

-- Example: Index of Multiple Deprivation style calculation
-- Normalize variables to 0-1 scale then combine
normalized_score = (var1_norm + var2_norm + var3_norm) / 3

Bivariate Mapping:

Shows relationship between two variables
Use 3×3 or 4×4 color grids
Effective for correlation analysis

Spatial Analysis Methods

Hot Spot Analysis:

Getis-Ord Gi* statistic
Identifies statistically significant clusters
Available through QGIS Processing Toolbox

Spatial Autocorrelation:

Moran’s I statistic
Tests for spatial clustering
Helps validate map patterns

Interactive Web Maps

Using QGIS2Web Plugin:

Install qgis2web plugin
Configure layer styling
Export to Leaflet or OpenLayers
Host on web server or GitHub Pages

Key Features for Web Maps:

Popup windows with detailed information
Layer switching capabilities
Zoom-dependent styling
Mobile-responsive design

Best Practices and Considerations

Data Privacy and Disclosure

Statistical Disclosure Control:

Small area data may be suppressed
Values less than 3 often masked
Rounded to nearest 5 or 10
Always check data quality statements

Cartographic Best Practices

Classification Considerations:

Avoid too many classes (5-7 maximum)
Consider data distribution
Use meaningful breakpoints where possible
Document methodology clearly

Color and Symbolism:

Test maps with colorblind simulators
Ensure accessibility compliance
Use appropriate color progressions
Consider cultural color associations

Technical Considerations

Performance Optimization:

Generalize boundaries for web mapping
Use appropriate file formats
Consider data size limitations
Implement progressive disclosure

Quality Assurance:

Validate data joins (check for missing values)
Verify geographic coverage
Cross-reference with known patterns
Peer review methodology

Common Challenges and Solutions

Data Integration Issues

Mismatched Geographies:

Use lookup tables provided by ONS
Be aware of boundary changes since 2011
Document any geographic adjustments

Missing Data:

Understand suppression rules
Consider aggregating to larger areas
Use alternative data sources where appropriate

Technical Challenges

Large Dataset Handling:

Use database connections rather than CSV files
Implement spatial indexing
Consider tile-based approaches for web maps

Cross-Platform Compatibility:

Test on multiple devices
Use web standards
Provide alternative formats

Advanced Applications

Time Series Analysis

Comparing with 2011 Census:

Account for boundary changes
Use consistent geographies
Consider population growth impacts

Trend Analysis:

Calculate change rates
Identify growth/decline patterns
Map demographic transitions

Policy Applications

Service Planning:

Catchment area analysis
Accessibility modeling
Demand forecasting

Resource Allocation:

Need-based distribution
Equity analysis
Impact assessment

Resources and Further Learning

Essential Documentation

ONS Resources:

Census 2021 User Guide
Geography User Guide
Statistical Disclosure Control methodology
Quality and methodology information

Online Communities

GIS Communities:

QGIS User Groups
GIS Stack Exchange
Reddit GIS communities
OSGeo forums

UK-Specific Groups:

AGI (Association for Geographic Information)
GISRUK (GIS Research UK)
ONS Geography user group

Training Opportunities

Formal Training:

University GIS courses
ONS Census training workshops
Commercial software training
Online certification programs

Sample Projects to Try

Population Density Mapping: Create a detailed population density map of your local area
Aging Population Analysis: Map areas with highest proportions of elderly residents
Educational Attainment: Visualize qualification levels across different regions
Housing Tenure: Analyze patterns of home ownership vs. rental
Commuting Patterns: Map travel-to-work flows and transport modes

The UK Census 2021 provides an unprecedented opportunity to understand contemporary British society through spatial analysis. By combining this rich dataset with GIS technologies, researchers, planners, businesses, and citizens can gain valuable insights into demographic patterns, social change, and local variations across the country.

Success in Census GIS mapping requires attention to both technical execution and thoughtful interpretation of results. Remember that maps are powerful communication tools that can influence decision-making, so always strive for accuracy, clarity, and appropriate context in your visualizations.

Whether you’re conducting academic research, supporting policy development, or simply exploring your local community, the techniques covered in this tutorial will help you unlock the analytical potential of the UK Census 2021 data through effective geographic visualization and analysis.

Last updated: August 2025 | This tutorial reflects current best practices for UK Census 2021 data analysis and visualization.