Prisons — how this layer is made

What you are looking at

Each dot is a prison. There are more than 14,000 worldwide. The size of a dot represents the area of the facility, and there is only one colour. Click on any of them to see what OpenStreetMap records, such as who runs it and whether the state or a company operates it. If there's a Wikipedia article, we show a short summary and a link to the full article, in your own language where possible.

Where the data comes from

Every facility here is something a mapper added at the OpenStreetMap website, from a survey, from local knowledge or from aerial imagery. We don't model or estimate anything ourselves, and we haven't merged in any national register of prisons.

What we include

We use one exact tag, `amenity=prison`. It covers everything OpenStreetMap files under that word, from a large state institution to a small detention building, and the tag itself does not distinguish between them. Because we match the tag exactly, a facility tagged as a prison and as something else at the same time falls out of the selection.

Colour

There is one colour, because OpenStreetMap records nothing about a prison that a legend could honestly rest on. The one candidate is a tag naming the operator. Fewer than one facility in ten carries it, and most of those say only that the government runs the place, so colouring by it would give one colour on a small part of the map and grey on almost all of the rest. There is no tag for capacity, none for security category and none for the type of facility. What the tags do record appears in the panel when you click a dot.

The perimeter at close zoom

Most prisons are mapped as the outline of their perimeter rather than as a single point, which is unusual on this site. At the closest zooms we draw that outline alongside the dot, so you can see the shape of the site as a mapper traced it. A prison is a walled compound of a size that shows clearly in aerial imagery, and that is what makes it straightforward to trace.

Size

The size of a dot represents the area of the facility in square metres. Because most facilities are traced, the size here is closer to a real measurement of the place than it is on most of our layers. It measures ground covered rather than the number of people held. A low-rise facility spread over open country draws larger than a taller one in a city that holds more people.

Where the map is empty

An empty area means nobody has recorded a facility there, not that a place has none. On this subject the gaps are not only a matter of how much mapping has been done. Prisons are politically sensitive in some countries, some facilities are deliberately absent from open data, some are mapped without a name, and mapping them is not without risk everywhere. So the places where the record is thinnest may be the places you most want to look at. Please do not read the density of this map as a measure of imprisonment.

Up to date, mostly

OpenStreetMap is edited continuously, and we take a new copy once every one to three months. A facility shown here may have closed, and a closed one keeps its buildings for years, sometimes in another use entirely.

Source and licence

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