Assumptions, calculations and sources
Baseline population: 69,483,900, the ONS mid-2025 estimate released on 1 October 2026, used as the latest official UK total available for this model. It is not a real-time population count. ONS source.
Minimum settlement count: ceil(69,483,900 / 50,000) = 1,390. Combined capacity 69,500,000, leaving only 16,100 spare places. Allowing for national population growth or keeping more headroom in each town would require more settlements.
Assumed town size: gross density 2,000 people/km², yielding a circular 25 km² envelope and 5.64 km diameter. This density and circular shape are modelling choices, not rules supplied by the user or scientific optimums. The envelope includes space for homes, business, public services, streets and internal green areas, without allocating their detailed land budgets.
Green gap: the 10-mile rule is interpreted as straight-line distance between the edges of final, fully expanded town envelopes. This equals 16.09344 km, making the required centre separation 21.73534 km. Measuring between centres instead would be a different rule.
Two layouts: a search over translated and rotated triangular grids places 540 fully coastal-contained town envelopes at the 10-mile edge gap. This demonstrates 27 million capacity; it is not a proven maximum. The comparison fits 1,390 envelopes at 13.4 km centre spacing, leaving 7.758 km / 4.82 miles between edges. This comparison explicitly changes the gap rule. It does not establish the largest possible feasible gap.
Separate geometric check: even allowing rearrangement, this circular model cannot accommodate 1,390 towns with 10-mile gaps. If the town radius is r and the edge gap is g, discs of radius r+g/2 around town centres cannot overlap. All such discs lie inside the UK outline buffered by g/2, including offshore buffer area. Hence:
N × π × (r + g/2)² ≤ area(UK buffered by g/2)
The buffered area is approximately 309,106 km². This gives an optimistic upper bound of about 830 towns (about 41.7 million capacity), already below the 1,390 required. This is a bound for the stated circular footprints and mapped outline, not a universal result for all shapes or densities, and not a claim that 830 suitable sites exist.
Land accounting: 1,390 × 25 = 34,750 km², about 14.3% of the mapped UK outline. The remaining land includes mountains, farms, habitats and other uses; it is not all freely available or equally useful. No food-yield, aquaponics, energy generation, storage, rainwater, drought, sewage, transport or health-service capacity has been demonstrated. Those require separate engineering and environmental models.
Permanent green zones: the scenario fixes the final town envelopes from the initial 5,000-person stage. Land outside them is excluded from later town expansion in the concept. This is not a map of existing legal protection. Existing green designations, protected landscapes, habitats, flood risk, ownership, productive agricultural soils, slopes and inland water have not been screened. Transport and utility links between settlements are not designed or drawn.
Whole-population counterfactual: existing towns and cities are not counted as additional inhabited places. This map shows a hypothetical end state; it does not model demolition, restoration of former urban land, construction emissions, relocation, financing or implementation time. No additional residents are assigned outside the town envelopes.
Geography and method: Natural Earth public-domain 1:10m national boundaries, projected to British National Grid (EPSG:27700). Town centres must lie inside the UK outline eroded by their final radius, so envelopes remain inside the mapped country. Coastlines are generalised. Distances are projected approximations and not survey measurements. Small islands that cannot hold the assumed footprint have no town. Rockall is outside the default map view.
Reproducibility: strict layout uses a 45° triangular lattice. The all-population layout uses a north-aligned lattice with 13.4 km centre spacing; eight surplus sites were removed with a fixed seed. All pairwise minimum distances were checked. Complete model assumptions and location coordinates are embedded in this file.
Built 13 October 2026. Interactive map: Leaflet 1.9.4, BSD 2-Clause. No external requests are needed to use this file.