A property check that used to mean reading 750 scanned maps.

1. The problem

Designated Protected Areas are rural and coastal places where the government restricts what a Shared Ownership leaseholder can do. Buy in one and you may never be able to staircase to full ownership, and you may be obliged to offer the property back to the housing association before selling on the open market. It materially changes what a home is worth.

Establishing whether an address falls inside one is genuinely awkward:

• The designation is defined by parish, in a schedule to a 2009 statutory instrument — not by postcode, and not by anything a buyer would recognise.
• Roughly 879 parishes are only partly designated, and the boundary for those exists solely as a scanned PDF map published by Homes England.
• Parish names repeat across counties. There are ~9,842 designated parish entries but only 8,957 unique names, so a name match alone is not safe.

In practice a conveyancer either skipped the check, or spent twenty minutes hunting a PDF and squinting at a boundary.

2. What we built

A free web tool that takes an address, a postcode, a pair of coordinates, or a pin dropped on a map, and returns an indicative DPA status with its reasoning, its sources and an honest certainty level attached.

The design decision that makes it fast: the entire dataset is baked into the container image as JSON. There is no database to query and nothing to go stale mid-request — a lookup is a dictionary hit. Around 91% of designated parishes are designated in their entirety, so for the large majority of addresses the tool can give a definitive answer without ever needing to consult a map.

For the partial parishes it does not bluff. It says the parish is partly designated, shows the relevant Homes England map, and tells the user the boundary needs checking by eye. Being clear about the limits of the answer matters more than appearing omniscient — every result is explicitly indicative guidance, not legal advice.

3. How it works now

A conveyancer pastes an address and gets a result page they can copy a link to, or print to PDF for the matter file. Behind it:

1. The address is resolved to coordinates and a parish, via postcodes.io and ONS Open Geography.
2. The parish is matched against the baked-in designation list — entire, partial, or not designated.
3. Partial matches are joined to the relevant map from the 750-PDF catalogue.
4. The verdict is rendered with its sources, its reasoning, and a shareable URL.

flowchart LR
    classDef extern fill:#fdfcfb,stroke:#c4873b,stroke-width:1.5px,color:#0a0f0f
    classDef hub fill:#0a0f0f,stroke:#c4873b,stroke-width:1.5px,color:#fdfcfb
    classDef out fill:#f3f2f1,stroke:#9a9a96,color:#0a0f0f

    A["Address, postcode,
coords or map pin"]:::extern
    G["postcodes.io +
ONS geography"]:::extern
    M["Homes England
750 map PDFs"]:::extern

    N["DPA Check
(baked-in dataset)"]:::hub

    R["Verdict + reasoning
+ sources"]:::out
    P["Shareable link /
printable report"]:::out

    A --> N
    G <--> N
    M --> N
    N --> R
    N --> P
      

No database. The designation data ships inside the image, so a lookup is a dictionary hit.

A scheduled job re-pulls the Homes England map catalogue every week and swaps it in atomically, so the tool cannot be left serving a half-updated dataset. Alongside the checker sit a national map overlay, the full 750-map catalogue, a JSON API, and fifteen explainer articles for the people arriving from a search rather than from a solicitor.

It is worth being straight about the limits. The map rasters are Crown copyright, so the tool points at them rather than redistributing them. And the output is written throughout as indicative guidance to inform a professional’s own check — never as a substitute for legal advice.