Concepts
Measures and periods
What a measure is
Each measure has an id you use in requests, like population, claimant-count or no2-background-mean, plus a label, a unit and a note of which areas and years it covers. Many come from the Office for National Statistics; others come from bodies like Ofcom and Defra.
A measure is published as it was released. If a publisher only covers England and Wales, so does the measure, and the API won't fill in the gaps.
Can it be added up?
Not every number can be combined. You can add up the populations of two councils, but you can't add up their median pay. Each measure declares which kind it is in its aggregation, and the API only offers totals, averages and conversions that make sense.
| Kind | What it is | Examples | What you can do |
|---|---|---|---|
extensive | Counts of things | Population, jobs, claimants | Add up over areas, and convert to other areas |
intensive | Shares, rates and averages | Broadband availability, air pollution | Average over areas, but only with the published weight the measure names |
non-aggregatable | Medians, ranks and similar | House prices, deprivation deciles, life expectancy | Use each area's value as it is |
Asking for something that doesn't make sense, like the total of a median, gets a clear 422 explaining why. See Errors.
A few measures are calculated by the Atlas rather than published directly, like population-density. Their values are marked derived, and the measure lists the datasets it was calculated from.
Periods
A period is the time a value describes, written the way the publisher writes it: 2022 for a year, 2026-04 for a month, or year-ending-2026-03 for a rolling year. A measure's catalogue entry lists every period it has.
Wherever period is optional, leaving it out gives you the latest one, and the response tells you it did.
Uncertainty
Some statistics are estimates with a margin of error. Where the publisher gives one, each value carries a confidenceInterval with its lower and upper bounds. The API never invents intervals of its own.
Useful endpoints
get/measuresList measuresget/measures/{measure-id}Get a measureget/measures/{measure-id}/qualityCheck a measure's quality