Curating local data for local people. In Bath.

Understanding Our Local Geographies

What is local data? For Bath: Hacked, local data means data about or relating to Bath & North East Somerset (B&NES).

But how is the B&NES region defined?

In this post I wanted to explore that question, paying particular reference to geography, or rather geographies, as there are several.

B&NES: a region and a council

B&NES as a district has only existed since 1996. As the Wikipedia page explains, the district was created after Avon was abolished.

The district is managed by B&NES council which is a Unitary Authority. Unitary authorities are essentially a combination of a county and district council and have responsibility for managing all functions in a region.

When we are referring to B&NES we may sometimes need to distinguish between the region - an administrative district of the UK and the council - the organisation that administers that district.

The District

The Bath and North East Somerset district covers 220 square miles (570 km2). The Ordnance Survey Linked Data site provides a nice overview of the area complete with a map showing the boundary as well as a list of the areas which it touches and contains. All of that data can be downloaded and explored directly from the site.

B&NES is neighboured by six other districts. B&NES is also part of Somerset, but confusingly Somerset is defined as both a “ceremonial county” which contains B&NES and a smaller administrative district which borders it.

Wards and Parishes

Electoral wards are the basic building blocks of the national administrative geography.

B&NES is broken down into 37 electoral wards. The list of wards and parishes is again listed at the official Ordnance Survey URL for B&NES, which links to each ward with details including a GML boundary region. The council also publishes a list of the wards, with links to PDF maps of the areas.

B&NES is also partially divided up into parishes. Bath itself doesn’t have any parishes, but the surrounding area is divided up into 51 parishes. Civil parishes are the smallest type of area in the UK administrative geography.

They also don’t necessarily correspond with the electoral wards. For example Keynsham is a Civil Parish but the same area is divided up across several wards, including Keynsham North and Keynsham South.

This highlights why we sometimes need to be careful when using statistics about local areas: the boundaries may be different depending on how the information was collected and reported.

Parishes and Wards are not the only type of area that overlap in the region


Postcodes are the geographical areas that we tend to bump into most often in our daily lives. Its the geographical identifier that we all typically have to hand. But postcodes are managed by the Royal Mail and are designed to support their mail delivery operations. This means that they regularly change as new houses are built, or Royal Mail alters its distribution. Post codes can also be changed and may be re-used in the future. So as stable geographical areas they aren’t necessarily ideal. Unfortunately its impossible to get post code boundaries as open data so things are even worse.

The Ordnance Survey do make some post code information available as open data. So from their Linked Data site we can find the list of 5750 postcode units in B&NES and this data has been added to the Bath Hacked data store. Postcodes are also organised into higher-level groupings. For example your home post code is a “postcode unit” whereas BA2 is a “postcode district”.

Postcodes don’t necessarily line up with electoral wards so they consist of yet another way to divide up the B&NES area.


Like Royal Mail, the NHS also divides up the UK into regions in order to support its operations. There are two types:

Statistical Areas

The Office of National Statistics uses its own geography for the purposes of publishing population statistics. The census geography is another hierarchical organisation of the UK. The smallest unit of which is the output area. The areas are sized so that they contain roughly equal numbers of people. This generally means around 125 households, although some are smaller. By dividing the UK into small regions, it becomes easier to identify changes to the population over time, whilst avoiding giving away any personal information.

Because output areas are sized based on the number of people living in them, they vary widely in how much actual land they include. Obviously rural output areas will tend to be larger, while the more densely populated city areas will be much smaller.

It’s possible to browse the statistical geography for B&NES using a tool provided by the ONS. On that page you can elect to see how the area is divided up into output areas, workplace zones, and middle and lower layer output areas. The

The ONS recently published a national address lookup dataset to help map between addresses and the various stiatistics, electoral, health and other geographies in use across the UK. The B&NES subset of this is available from the Bath: Hacked datastore.

Fire, Police, Ambulance Services

To be comprehensive its also worth noting that the fire, ambulance and police services in the UK also have their own geographical breakdowns. Again, like the health and mail services, these reflect organisational jurisdictions.

As a quick reference, B&NES is covered by


There are a number of different national geographies that cover our local area. When working with local data it’s important to understand the differences between them, especially when it comes to comparing statistics published by different organisations.

Hopefully this blog post provides some useful insight and pointers to further reading.