England Green Infrastructure Mapping Database

Executive Summary 

Axion Solutions was commissioned by Natural England to deliver the first national quintennial Change Detection Reporting Exercise for the England Green Infrastructure Mapping Database (EGIMD). 

The project represents the first formal five-year change assessment of England’s Green Infrastructure (GI) asset base, comparing three EGIMD versions (V1, V2.1 and V2.2) to: 

• Establish a QA-assured national baseline. 
• Quantify statistical change across England’s Green Infrastructure. 
• Distinguish genuine landscape change from data and geometry artefacts. 
• Develop a repeatable methodology for future five-year reporting cycles. 

The commission delivered a nationally scalable, automation-enabled spatial workflow that: 

• Harmonised all datasets to June 2025 Local Authority boundaries. 
• Integrated Change Registry polygon tracking. 
• Applied refined QA thresholds and sliver-removal logic. 
• Produced England-wide statistical summaries and interpretation-ready outputs. 

The result is the first defensible, auditable national evidence base demonstrating how England’s mapped Green Infrastructure is changing over time—establishing EGIMD as a credible long-term monitoring instrument. 

Strategic and Programme Context  

The EGIMD has been developed since 2020 to provide a consistent, national spatial register of Green and Blue Infrastructure assets. Its core purpose includes enabling long-term monitoring of: 

• Combined Green and Blue Infrastructure Assets (Module 1). 
• Accessible Green Infrastructure (AGI). 
• Accessible Greenspace inequalities. 
• Likely Accessible Waterside. 

The first change detection exercise was triggered by the publication of EGIMD Version 2.2, creating three temporal “snapshots” across approximately five years. 

This commission supports: 

• The Natural Capital & Ecosystem Assessment (NCEA) programme. 
• National GI policy development. 
• Local Nature Recovery Strategy (LNRS) evidence requirements. 
• Future statistical QA and monitoring functions within Natural England. 

The objective was not simply to calculate change, but to establish whether detected change represented: 

1. Data improvement and quality refinement. 
2. Typological reclassification within stable geometries. 
3. Genuine land-use and infrastructure change on the ground. 

This distinction was fundamental to ensuring policy credibility. 

The Challenge: Detecting Real Change at National Scale 

Delivering the first quintennial change detection exercise presented several structural challenges: 

1. Multi-Version Data Complexity 

Three separate EGIMD versions required alignment, reconciliation and harmonisation across: 

• Differing Local Authority boundaries. 
• Evolving typologies. 
• Improvements in source datasets. 

2. Geometry and Artefact Risk 

National-scale overlay processes can introduce: 

• Sliver polygons. 
• Coastal buffer shifts. 
• CRS inconsistencies. 
• Large artefactual geometries masking real signal. 

Without rigorous QA logic, these artefacts risked misinterpretation as genuine GI growth or loss. 

3. Interpreting Change Causality 

The Change Registry recoded polygons as New, Removed, or Unchanged, but did not explain why change occurred. 

The project therefore required sampling, visual inspection, and typological cross-analysis to differentiate: 

• Dataset refinement 
• Reclassification 
• Actual spatial change 

4. National Scaling 

The workflow had to operate consistently across: 

• England 
• LNRS areas 
• 320+ Local Authorities 
• Protected Landscapes (National Parks, National Landscapes, Heritage Coasts) 

The solution required automation without sacrificing interpretability. 

The Project Process: A Structured Four-Task Framework 

Axion delivered the commission through a structured methodology aligned to the RFQ specification. 

Task 1 – Statistical Review and Baseline QA 

Objectives: 

• Re-extract Version 1 statistical tables directly from spatial data. 
• QA-check Version 2.1 and Version 2.2 published tables. 
• Harmonise all outputs to June 2025 Local Authority geographies. 

Process: 

• Automated spatial extraction scripts (Python / Model Builder). 
• CRS standardisation to EPSG:27700 (British National Grid). 
• ≥10% stratified manual spatial sampling. 
• Cross-version reconciliation checks. 

Outputs: 

• England, LNRS, Local Authority, and Protected Landscape summaries. 
• Verified national baseline dataset. 
• QA-signed statistical assurance documentation. 

This established a statistically robust platform for change comparison. 

Task 2 – Change Registry Validation 

Task 2 stress-tested the change detection workflow using two contrasting test authorities: 

• Medway (coastal context) 
• Peterborough (urban inland context) 

Objectives: 

• Validate overlay logic between V1 and V2.2. 
• Test sliver removal thresholds. 
• Assess large-polygon change logic. 

QA Enhancements: 

• Sliver removal threshold (<0.05 ha). 
• Revised large-change flag (>10 ha, replacing >500 ha). 
• Visual validation via aerial imagery and QGIS. 

The method was confirmed as auditable and repeatable. 

Task 3 – National Roll-Out 

Following validation, the workflow was scaled nationally. 

Key Actions: 

• Automation of overlay and QA flag generation. 
• Processing across 320+ Local Authorities. 
• Creation of England-wide change polygons. 
• Generation of summary CSV outputs. 

Deliverables Included: 

• National shapefile of change polygons. 
• Area-change statistics by Local Authority. 
• QA variance tables. 
• Reusable change detection model. 
• National QA technical report. 

QA outcomes confirmed: 

• Geometry artefacts negligible at national scale. 
• Large changes systematically flagged and reviewed. 
• No evidence of systematic bias. 

Task 4 – Interpretation, Causality and Reporting 

Task 4 focused on policy-ready interpretation. 

Key Interpretative Themes: 

• Typology-level change patterns. 
• Distinction between data refinement and land-use change. 
• Spatial coherence of national patterns. 
• Coastal change narrative (requiring careful contextualisation). 

Emergent patterns showed: 

• Net national AGI growth detectable and spatially coherent. 
• Change concentrated in a limited number of authorities. 
• Coastal adjustments explainable through geometry updates rather than loss. 

The interpretation phase translated statistical outputs into defensible national narratives. 

Quality Assurance and Procedural Rigour 

QA formed the backbone of the programme. 

Geometry QA: 

• 100% validity confirmed via Fix Geometries tools. 
• CRS alignment to EPSG:27700. 
• Sliver removal (<1% removed nationally). 

Registry QA: 

• Verification of New/Removed/Unchanged classification logic. 
• Sampling of flagged >10 ha changes. 

Governance: 

• Steering Group review checkpoints. 
• Transparent documentation of thresholds. 
• Reproducible automation models are retained for future cycles. 

Success criteria included ensuring change patterns were: 

• Structured 
• Explainable 
• Free from random processing noise 

These criteria were met. 

Mapping and GIS: Structuring Strategic Action 

The project transformed EGIMD from a static spatial dataset into a dynamic monitoring instrument. 

Key technical components included: 

• Polygon-level overlay analysis. 
• Typology cross-tabulation. 
• Multi-geography aggregation. 
• Reusable QGIS / Python automation models. 

The Change Registry system now functions as a longitudinal tracking mechanism, enabling future five-year comparisons to be executed efficiently with established QA logic. 

Project Conclusions: Impact and Learning 

The First Quintennial Change Detection Exercise achieved four critical outcomes: 

1. Established a National Baseline 

England now has its first QA-assured five-year GI change benchmark. 

2. Proved Methodological Robustness 

The workflow reliably distinguishes: 

• Real GI growth 
• Typology reclassification 
• Data refinement artefacts 

3. Demonstrated EGIMD Sensitivity 

The database is responsive to genuine landscape change without generating systemic false positives. 

4. Enabled Future Iterations 

The methodology is designed for repeatable ~5-year cycles, forming the operational foundation for future V2.3+ comparisons. 

Reflections and Long-Term Legacy 

This commission represents a maturation point for national Green Infrastructure monitoring in England. 

By combining statistical extraction, spatial overlay logic, Change Registry analysis and structured QA, the project: 

• Established EGIMD as a defensible national monitoring tool. 
• Created confidence in data-driven GI policy. 
• Provided Natural England with a scalable analytical pipeline. 

The legacy of this work is not simply a report—it is a repeatable national monitoring framework. 

Future iterations will build upon: 

• Refined QA thresholds. 
• Typology-level disaggregation. 
• Change attribution analysis. 
• Dashboard visualisation for area teams. 

The First Quintennial Change Detection Exercise therefore transitions EGIMD from a mapping product into a living national evidence system—capable of tracking England’s Green Infrastructure with clarity, confidence and methodological integrity.