ONS Open Geography Portal
The ONS Open Geography Portal provides UK geographic boundaries, lookups, and postcode data
via ArcGIS REST services hosted by the Office for National Statistics.
Data Model
- ONSPD — ONS Postcode Directory. Maps postcodes to every geographic classification (LAD, LSOA, MSOA, region, constituency, health area, etc.). Updated quarterly.
- LAD — Local Authority Districts. Administrative boundaries with codes, names, and centroids. Multiple vintages available (e.g. LAD_MAY_2025_UK_BFC_V2).
- Boundary services — Hundreds of services covering wards, parishes, counties, regions, constituencies, health areas, census output areas, built-up areas, and more.
- Lookup tables — Cross-reference between geographies (e.g. OA to LSOA to MSOA to LAD).
Key Patterns
- All services use ArcGIS REST query syntax: where, outFields, f=json, resultRecordCount.
- Use SQL-like where clauses: LAD25NM LIKE '%Manchester%', pcds='SW1A 1AA'.
- Set returnGeometry=false for attribute-only queries (much faster, smaller response).
- Service names follow ONS conventions: {TYPE}_{DATE}_{COVERAGE}_{BOUNDARY_TYPE}.
- Boundary types: BFC (Full Clipped), BFE (Full Extent), BGC (Generalised Clipped), BSC (Super Generalised), BUC (Ultra Generalised).
- NC = Names and Codes (no geometry, just reference data).
Field Naming
- Postcode fields: pcds (display format, e.g. "SW1A 1AA"), PCD7/PCD8 (fixed-width).
- LAD fields: LAD25CD (code), LAD25NM (name), LAD25NMW (Welsh name). Year suffix matches the vintage.
- Geographic codes: Follow pattern {TYPE}{YY}CD for code, {TYPE}{YY}NM for name.
Gotchas
- No auth: Completely open API. Be respectful of rate limits.
- Service names change: New vintages are published periodically with updated year suffixes. The tools use the latest known working names.
- Large responses: Boundary geometry can be very large. Use returnGeometry=false when you only need attributes.
- Result limits: ArcGIS caps results at 2000 per query by default. Use resultRecordCount and resultOffset for pagination.
- URL encoding: Service names with parentheses and spaces must be URL-encoded.
