WARNING: This is under development and may not function correctly.

Population calculator

Usage

To use the tool, you need to create an area on the map. There are three ways to create an area:

Click the at the top-left of the map to draw a circle with a set radius;
Click the at the top-left of the map then draw an area;
Click the icon to search for outlines of a UK local authority, ward, or constituency from the Office of National Statistics or find an administrative outline from OpenStreetMap;
Drag-and-drop a GeoJSON file onto the map.

Once you have an area drawn on the map, click the "Calculate!" button.

Notes

This tool finds the population within polygons or circles. It is based on the original Population Around A Point tool by Tom Forth.

The data is the Global Human Settlement Layer population grid for 2025. This release was known to be less accurate for small areas, especially where there has been rapid change in population.

The bus stop, tram stop, and train/metro stop data is from Open Street Map from early 2023 and has errors. Many stops are missing, especially outside of Europe. Stops included rarely used or heritage service stops.

The maximum circle radius is set to 100km, it would get slow above that. The minimum radius is set to 3km because otherwise some city-centre populations are likely to be very wrong and Tom can't be bothered fielding all the "your amateurish tool gives completely spurious information and you should be ashamed of yourself!" type comments that would generate.

This tool then queries Tom's API. Here's how Tom makes this data:

Convert the GeoTIFF files from the GHSL into populations at points.
Load these points into an SQLite database.
Add a compound index (on latitude and longitude) to this SQLite database so that lookups are very fast.
Create an API in C# ASP.NET running on an Azure Web App that does some geographical processing and queries the SQLite database to calculate the population within any distance of any location.

Credits

This open source project is made possible thanks to other open source and open data projects:

Inspired by an existing project by Thomas Forth / imactivate. This version by Open Innovations - code on GitHub (MIT licence). Please report bugs with some information to help use recreate them.
Uses Leaflet, a modified version of leaflet-area-selection, and Leaflet.draw.
Place labels uses our Leaflet.PlaceNameLayer.js with names sourced from GeoNames.
Location lookup uses city/town data from GeoNames (CC-BY).
UK geography outlines from ONS (using our Geography Bits repository).
Icons by Bootstrap (MIT licence).