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Which population figure is right?

By James Burfield, SEO consultant, Bath · Page updated 18 September 2026

All of them, usually. A place can have three or four populations that are each entirely correct, because each measures a different boundary. This is the single biggest source of disagreement between published population figures, and most sources never say which one they used.

The four boundaries

Boundary	What it covers	Who defines it
The place	The settlement itself, roughly its built-up core. The everyday sense of a town.	No single authority. Ours come from GeoNames.
The local authority	The council area. Often takes in neighbouring towns and a good deal of countryside.	Statute. ONS publishes the estimates.
The built-up area	Continuous development, where buildings sit less than 200m apart.	ONS Census 2021. We hold these for England outside London, and Wales.
The agglomeration	The wider urban mass, including places that have grown into each other.	Varies. Ours are the World Gazetteer's 2005 definitions.

There is no correct choice among these. There is only a stated one and an unstated one.

Built-up area figures cover England excluding London, and Wales. ONS could not identify individual settlements inside Greater London with this method and removed its 33 built-up areas from the analysis; Scotland and Northern Ireland define settlements differently, so merging them in would be a false equivalence. Where we hold no BUA figure, the row simply does not appear.

Worked examples

London

What you mean	Population	Source
The place itself The populated settlement, roughly the built-up core.	8,961,989	GeoNames
The agglomeration The continuous urban area, including places that have grown into it.	12,599,561	World Gazetteer (2005)
The place in 2005 The same settlement twenty years earlier.	7,421,209	World Gazetteer (2005)

London in full →

Leeds

What you mean	Population	Source
The place itself The populated settlement, roughly the built-up core.	536,280	GeoNames
The local authority The Leeds council area, which can take in surrounding towns and countryside.	845,189	ONS mid-year estimate (2024)
The agglomeration The continuous urban area, including places that have grown into it.	1,880,819	World Gazetteer (2005)
The place in 2005 The same settlement twenty years earlier.	455,123	World Gazetteer (2005)

Leeds in full →

Reading

What you mean	Population	Source
The place itself The populated settlement, roughly the built-up core.	318,014	GeoNames
The local authority The Reading council area, which can take in surrounding towns and countryside.	182,907	ONS mid-year estimate (2024)
The built-up area Continuous development, where buildings sit less than 200m apart. Drawn from where the buildings are, not where the council boundary is.	203,795	ONS Census 2021 (2021)
The place in 2005 The same settlement twenty years earlier.	244,070	World Gazetteer (2005)

Reading in full →

Conwy

What you mean	Population	Source
The place itself The populated settlement, roughly the built-up core.	3,873	GeoNames
The local authority The Conwy council area, which can take in surrounding towns and countryside.	114,891	ONS mid-year estimate (2024)
The place in 2005 The same settlement twenty years earlier.	3,890	World Gazetteer (2005)

Conwy in full →

Where the gap is widest

These are the places where our current figures diverge most between definitions. Every row is a place whose population you could state two ways and be right twice.

Place	County	As a place	As an authority	Gap
Halton	Borough of Halton	2,218	131,543	59.3×
Conwy	Conwy	3,873	114,891	29.7×
Caerphilly	Caerphilly County Borough	31,060	176,865	5.7×
Wokingham	Wokingham	41,143	187,200	4.5×
Falkirk	Falkirk	35,310	160,020	4.5×
Wigan	Borough of Wigan	175,405	344,922	4.2×
Warwick	Warwickshire	37,267	154,889	4.2×
Walsall	Walsall	172,141	295,678	4.2×
Southwold	Suffolk	3,680	—	3.9×
Rotherham	Rotherham	117,618	276,595	3.9×
Harby	Nottinghamshire	250	—	3.9×
Leatherhead	Surrey	43,544	—	3.8×

Compare two places

Comparing places only means anything if both figures use the same boundary. Put two places side by side and see them under each definition at once.

Why we make a fuss about this

Because it is the difference between a number you can cite and one you cannot. When we added a 2005 comparison to our place pages, 58 of them showed growth that was pure boundary artefact: Preston appeared to have grown 64%, Swansea 76%. Neither had. Those figures are now suppressed and labelled rather than published.

Further reading: how many people live in London (four correct answers, nine million apart) and what a built-up area is.

Common questions

What is the difference between a city and a town in the UK?

A city holds letters patent from the monarch; there are exactly 76. A town has no legal definition at all. Size plays no part in either, which is why St Davids is a city at under two thousand residents and Reading is not at over three hundred thousand.

Why do population figures for the same place differ?

Because a place has several honest boundaries: the local authority, the built-up area drawn from where buildings stand, and the everyday settlement. Each carries a different figure, and most published lists mix them without saying which they used.

What counts as a built-up area?

Land ONS classes as irreversibly urban from Ordnance Survey data, with buildings generally under 200 metres apart. It follows the bricks rather than the council boundary, which is why it is usually the figure people mean and rarely the one they quote.

Which population figure should I use?

The one whose boundary matches your question, stated alongside the number. Comparing places needs one geography for every row. Policy questions want the local authority, because that is the unit with a council and a budget. Quoting a figure without its boundary is how lists end up disagreeing.