How we know this

Gaz answers questions about the United Kingdom's constituencies using only public data, and shows you where every figure comes from. No number appears without its source; when a figure is modelled or missing, we say so rather than guess.

How an answer is built

1. Resolve. A postcode, place, or MP name is matched to a constituency deterministically – the model never guesses the area.
2. Query. Only allow-listed, read-only queries run against the data warehouse. There is no free-form database access.
3. Cite. Every figure is returned with its source and an honest quality flag.
4. Guardrail. Gaz states only the numbers the data returns, declines gaps and forecasts, and suppresses very small counts.

Data sources

What the quality flags mean

Complete:

Complete, exact, and current.

Partial coverage:

Some areas or categories are missing from this source, so treat it as partial.

Modelled estimate:

This figure is estimated and apportioned onto the constituency, not measured directly.

Data gap:

This data isn't available for this area, so it is shown as a gap rather than guessed.

Two crime lenses, never mixed

Crime is shown through two separate sources that are never added together. The street feed (data.police.uk) is monthly and grouped into broad categories. The ONS offence splits are annual and give the finer offence groups the street feed lacks (homicide, sexual offences, drugs). They cover different periods from different publishers, so the Gazetteer reports each on its own and never sums or directly compares them.

Honest granularity. Common offences are apportioned to the constituency by population share and flagged modelled. Rare or sensitive offences – homicide and sexual offences – are too few to split to a single seat without inventing precision, so they are shown at the council level ONS publishes, with that caveat, rather than as a fabricated per-seat number.

Who's responsible? (My Area)

The My Area page turns a postcode into the bodies responsible for it. The council, police force, NHS board, fire service and waste authority come from official ONS geography lookups and are shown as Grade A – named, official, organisation-level data. In two-tier areas we show both the district and the county council with what each does (planning and bins vs roads and social care), because responsibility is genuinely split.

Councillors come from Democracy Club (CC BY 4.0), a community-maintained source. We label them Grade C and show the date each record was last updated, because community data can lag a by-election or a co-option. We show this rather than leave councillors out – but we are honest that it is less authoritative than the official bodies, and we link back to Democracy Club as the source. Spotted something wrong? Tell us and we will check it.

The transport authority (the Local Transport Authority, per the Transport Act 2000) is shown as Grade B – modelled, because no single official file maps an area to its transport authority. We derive it from official inputs – London is Transport for London; combined-authority areas are the combined authority; two-tier shire areas are the county; unitaries are themselves – and reconcile it against the Department for Transport's own list of funded transport authorities (so a newly-created combined authority that does not yet run transport correctly falls back to the council that does).

In Scotland the transport body is one of the seven Regional Transport Partnerships (established by the Transport (Scotland) Act 2005), and in Wales it is one of the four Corporate Joint Committees, which hold regional transport planning as a statutory function (the 2021 CJC regulations). There is no official file mapping councils to either, so – as in England – we build the membership by hand from the founding legislation (one body per council by statute) and show it as Grade B – modelled. One council is split in statute: Argyll & Bute sits mostly in HITRANS (with Helensburgh & Lomond in SPT); we show the whole council as HITRANS and note the overlap.

Your water and sewerage companies (often different in England – a water-only company may supply your water while the regional company handles sewerage) are found by locating your postcode inside Ofwat's official company boundary maps (digitised by Ofwat with Ordnance Survey, Open Government Licence). Because a postcode is an area and the boundary is not the legal record, we show this as Grade B – modelled: it is the company's area, and your specific property may differ (some developments are served by a separate new-appointment provider). In Scotland both are Scottish Water, the single national provider (Grade A).

Known gaps, stated plainly

• Scotland has no open street-level crime feed, so Scottish crime is shown as a gap, not estimated from England's data.
• The open crime feed merges violence and sexual offences; the disaggregated splits (homicide, sexual offences, drugs) come from ONS council/CSP-level tables apportioned to constituency and flagged modelled – with rare offences kept at council level (see “Two crime lenses” above).
• England & Wales census figures and Scottish house prices are apportioned onto constituencies, so they are flagged modelled – accurate nationally, estimated locally.
• Time series spanning the 2024 boundary review are approximate.
• Councillor names are community-sourced (Democracy Club, Grade C) and dated; parish and town councils are not included, and county-division councillors in two-tier areas are coming soon. The councils themselves (district, county, unitary) are Grade A.

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