How Siteline knows what it knows
Siteline is built on one rule: a deterministic engine reads official data, and everything you see traces back to a named source. Nothing is scraped from listings, nothing is estimated by a language model, and where the data runs out we say so rather than rounding the corner.
The constraint check
Conservation-area and Article 4 boundaries are published as geometry by planning.data.gov.uk. We ingest each covered borough's polygons (refreshed monthly — the data changes slowly) and, when you enter a postcode, test its coordinates point-in-polygon against those boundaries in-process. The result names the designation and links the dataset. A point check is indicative: postcode centroids sit metres from front doors, and boundaries can run mid-street — near an edge, we say so, and the council's own map remains the legally definitive source.
Prices and comparables
Sold prices come straight from HM Land Registry Price Paid Data — real transactions, by postcode, with dates and tenure. Borough-level averages use the UK House Price Index. PPD carries no floor areas, so we never quote £/sqm from it; cost per square metre comes from the Hampstead Renovations project ledger instead, always as a low/expected/high range, never a single number.
Confidence tiers
Every major answer carries a tier. High: structured data matched to your location — a constraint boundary, a sold price. Medium: present but interpreted — cost ranges, uplift directions. Low: incomplete data or local judgement needed — flagged for manual review rather than papered over.
What the AI is allowed to do
A language model writes plain-English explanations of facts the engine has already established — that is its entire job. It is never permitted to invent constraints, approvals, prices, application references or legal conclusions, and its output must cite the source records it was given. If data is missing, it must say missing.
What we won't claim
Siteline provides planning and cost intelligence for early feasibility only. It is not legal, planning, valuation, architectural, structural or surveying advice; planning outcomes are decided by local authorities, and every estimate here is a range to be verified by qualified professionals before you commit money. If a number on this site ever looks too precise to be honest, tell us.
The data, named
| planning.data.gov.uk | Conservation-area and Article 4 direction boundaries — official geometry, ingested per borough and refreshed monthly. |
| HM Land Registry Price Paid Data | Real sold-price transactions by postcode — the comparables behind every uplift discussion. |
| HM Land Registry UK House Price Index | Borough-level average prices, annual change and sales volumes on borough pages. |
| postcodes.io | Postcode and district geocoding — coordinates, borough, ward. |
| Planning London Datahub | London-wide planning applications — powering precedent search as it rolls out. |
| Hampstead Renovations project ledger | Real build-cost data from delivered North London projects — the calibration behind every cost range. |
Contains public sector information licensed under the Open Government Licence v3.0.