These posts are as much about me remembering what I coded, how and where the data came from!

The term deprivation often appears in policy papers, health studies, and now on data websites like this one.  It measures how much an area falls behind others in terms of income, employment, education, health, housing, access to services, crime, and the living environment.  It is a structured measure based on real statistics, not a label about individuals.

To understand it properly, you have to look at how the data is built, how it links to postcodes, and why there are differences across England, Wales, Scotland, and Northern Ireland.

The Core Datasets

Each country of the UK publishes its own version of the Index of Multiple Deprivation (IMD).  Although they share a similar method, they are created independently and released on different schedules.

• England: Index of Multiple Deprivation (IMD) — maintained by the Department for Levelling Up, Housing and Communities (DLUHC).
• Wales: Welsh Index of Multiple Deprivation (WIMD) — published by the Welsh Government.
• Scotland: Scottish Index of Multiple Deprivation (SIMD) — managed by the Scottish Government.
• Northern Ireland: Northern Ireland Multiple Deprivation Measure (NIMDM) — published by NISRA.

Each dataset provides at least two key tables:

1. A ranked list of all small areas (LSOAs, Data Zones, or SOAs), where 1 = most deprived and the maximum number = least deprived.
2. A domain breakdown, showing separate scores for each domain such as income, employment, education, health, housing, crime, and environment

These are published as CSV files and often accompanied by metadata documents explaining how each indicator is built and what data sources were 

How the Geography Works

The IMD does not measure deprivation for individual people or postcodes.  It measures it for small geographic areas.

In England and Wales, these are Lower Layer Super Output Areas (LSOAs).  Each LSOA covers roughly 1,500 residents or 650 households.  Scotland uses Data Zones, and Northern Ireland uses Super Output Areas (SOAs).

Every LSOA or equivalent has a GSS code, for example:

• E01000001 (England)
• W01000396 (Wales)
• S01006514 (Scotland)
• N00000104 (Northern Ireland)

The prefix letter identifies the nation, and the rest of the code is a numeric identifier.

These codes are managed by the Office for National Statistics (ONS) and stored in several open datasets, the most important being the ONS Postcode Directory (ONSPD).

Connecting Postcodes to Deprivation Data

Postcodes are how most people search for data, but deprivation indices are built around small area codes, not postcodes.  The ONSPD is what makes it possible to bridge the two.

The ONSPD is updated quarterly and can be downloaded from ONS Geography.  It links every live and terminated postcode in the UK to dozens of geographic layers, including:

• LSOA, MSOA, Local Authority, Region, Country
• Clinical Commissioning Group (CCG)
• Census Output Areas
• Parliamentary Constituency
• Eastings and Northings coordinates (for mapping)

To link deprivation data to postcodes, you merge the IMD table with the ONSPD using the LSOA code.  For example:

1. From the IMD CSV, take each LSOA code and its rank or score.
2. From the ONSPD CSV, take each postcode and its LSOA code.
3. Join on the LSOA code.

The result is a dataset where every postcode inherits the deprivation rank of its LSOA.  This is how the site’s postcode search works for England, Wales, and Scotland.

Why It Does Not Work for Northern Ireland

Northern Ireland is different because its postcodes are managed separately by Royal Mail and NISRA, and the government does not release a public lookup that connects postcodes to SOAs.

While the NIMDM data itself is public, the link between postcodes and those small areas is not openly licensed.  Commercial datasets exist, but they cannot be shared or published freely.

Because of this, the site can still display Northern Ireland deprivation maps and regional rankings, but cannot provide postcode searches.  That is not a technical limitation, it is a licensing one.

How the Maps Are Built

Each nation provides boundary shapefiles for its small areas.  These are geospatial files that describe the polygon boundaries for every LSOA, Data Zone, or SOA.

For example:

• LSOA boundaries (England and Wales)
• Data Zones (Scotland)
• SOA boundaries (Northern Ireland)

Each shapefile is a .shp file, often distributed in a ZIP folder with .dbf, .shx, and .prj components.  These files are read into GIS tools like QGIS or converted into GeoJSON format for use on the web.

A typical conversion process looks like this:

The .dbf file contains attribute data, including the GSS codes.  When converted, each polygon in the GeoJSON contains a code field (for example, “E01000001”), which can be matched with the IMD table to apply the correct rank and colour.

On this site, the polygons are simplified to reduce file size, then stored in the public/geo/ directory.  When a user opens a map, the relevant file is loaded, and the JavaScript layer colours each area based on its rank.

Understanding the Scoring System

Each small area is given:

• A raw score, a weighted sum of all domain indicators.
• A rank, from 1 (most deprived) to N (least deprived).
• A decile or quintile, which groups areas into 10 or 5 bands nationally.

The English index uses the following domain weights:

These domains are weighted to create an overall deprivation score for each area.  The results are relative, not absolute — a rank of 1000 does not mean “half as deprived” as 500, it only means it is further down the list.

Interpreting the Maps

When viewing deprivation maps, darker colours indicate higher deprivation.  The shading is usually based on deciles, meaning the top 10 percent of areas are shown darkest.

A common mistake is to interpret this as “everyone in that area is deprived”.  The correct interpretation is that the average conditions in that small area are worse than in most others, based on the combined indicators.  Even within the most deprived areas, there are households doing well, and within the least deprived areas, there are households struggling.

Data Limitations and Updates

Deprivation indices are not updated every year.  The English IMD was published in 2019 and then 2025, the Welsh index in 2019, the Scottish index in 2020, and the Northern Ireland one in 2017.  Each update is a major statistical exercise, combining hundreds of data sources, so new releases come roughly every five to six years.

Between releases, the rankings do not change, even though conditions on the ground might.  This means the maps show relative deprivation at the time of publication, not in real-time.

Why It Matters

Deprivation data feeds directly into how resources are allocated across the UK.  It helps government departments, local councils, and research bodies understand where to focus support for housing, health, education, and economic development.

For example:

• NHS England uses IMD scores to study health inequalities.
• The Department for Education uses them to allocate funding to schools.
• Local authorities use them to design regeneration and housing programmes.

For the public, being able to view and understand this data through postcodes, maps, and charts helps make sense of complex national statistics that would otherwise remain buried in spreadsheets.

Summary

Deprivation measurement in the UK is built from the ground up:

• Small geographic units (LSOAs or equivalents) form the base.
• Each is assigned a GSS code.
• Deprivation ranks are published by each nation.
• The ONS Postcode Directory links those codes to postcodes.
• Shapefiles define the physical boundaries for mapping.
• GeoJSON files bring those boundaries online for interactive maps.

Together, these datasets form a complete, transparent, and factual picture of how different areas compare.  What you see on the map is not speculation or opinion, it is government data processed and presented for clarity and understanding.