markmclaren/inspired-postcodes

Inspired Postcodes

GB postcode boundary polygons derived from open Land Registry and ONS data, published as PMTiles vector tile files.

Interactive map: markmclaren.github.io/inspired-postcodes

The approach was inspired by Mark Longair's blog post: Open Data GB Postcode Unit Boundaries

Mark's Voronoi-processed postcode data, derived from Mapit, is also available as PMTiles: github.com/markmclaren/mapit-postcode-pmtiles — live viewer

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Files

File	Layer name	Description
inspire_original.pmtiles	inspire	All INSPIRE property boundary polygons. Where a parcel spans multiple postcodes, it is split into segments using Voronoi cells seeded from UPRN coordinates. No-postcode parcels are retained.
inspire_single_pcds.pmtiles	inspire	Property parcels that map cleanly to exactly one postcode. Parcels with multiple or unresolved postcodes are excluded.
inspire_dissolved_pcds.pmtiles	pcds_dissolved	Postcode unit boundaries (e.g. AB10 1AB), formed by dissolving all single-postcode parcel geometries by postcode.
inspire_sector_dissolved_pcds.pmtiles	pcds_sector_dissolved	Postcode sector boundaries (e.g. AB10 1), formed by dissolving the unit boundaries.
inspire_district_dissolved_pcds.pmtiles	pcds_district_dissolved	Postcode district boundaries (e.g. AB10), formed by dissolving the sector boundaries.
inspire_area_dissolved_pcds.pmtiles	pcds_area_dissolved	Top-level postcode area boundaries (e.g. AB), formed by dissolving the district boundaries.

All parcel-level layers (inspire_original, inspire_single_pcds) include the following properties:

Property	Description
pcds_single	The single postcode assigned to the parcel (e.g. AB10 1AB).
uprn_count	Number of UPRNs within the parcel.
pcds_count	Number of distinct postcodes within the parcel.
colour_index	Integer (0–5) for neighbour-contrast polygon colouring.

Dissolved layers include the postcode key for their level (pcds, pcds_sector, pcds_district, or pcds_area) plus source_unit_count and source_polygon_count.

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How the Data Was Produced

The pipeline was run on the Isambard 3 HPC system using a set of Python/DuckDB scripts and Slurm job definitions.

1. Download INSPIRE GML zip files (one per local authority, ~318 councils for England and Wales) from the HM Land Registry INSPIRE download service.
2. Load each GML into DuckDB via GDAL/ST_Read, with offline GML sanitisation to avoid remote schema fetches on HPC compute nodes.
3. Enrich polygons with postcode data by spatially joining NSUL UPRN points (converted from EPSG:27700 to WGS 84) onto each parcel.
4. Split multi-postcode parcels by constructing Voronoi cells from the UPRN point coordinates within each parcel and intersecting them with the original polygon.
5. Export to newline-delimited GeoJSON per council.
6. Tile each GeoJSON to MBTiles with Tippecanoe (zoom 0–16, geometry simplification, no tile size limit to prevent feature dropping at low zoom).
7. Merge all per-council MBTiles with tile-join, then convert to PMTiles with the pmtiles convert CLI.
8. Dissolve the single-postcode merged layer progressively by postcode unit, sector, district, and area (with a 2 m buffer to close small gaps between adjacent parcels before union), producing four dissolved PMTiles outputs.

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Data Sources

• INSPIRE Index Polygons — HM Land Registry Cadastral Parcel data for England and Wales. use-land-property-data.service.gov.uk/datasets/inspire

• National Statistics UPRN Lookup (NSUL) — ONS dataset mapping Unique Property Reference Numbers (UPRNs) to postcodes and British National Grid coordinates (December 2025, Epoch 123). geoportal.statistics.gov.uk/datasets/4e0b4b3fbc2540caae27e7be532e61be

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Licence

Contains HM Land Registry data © Crown copyright and database right 2025.
Contains National Statistics data © Crown copyright and database right 2025.
Licensed under the Open Government Licence v3.0.