Open Geography Portal

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.