Prisons — how this layer is made

What you are looking at

Each point is a prison — a feature tagged `amenity=prison` in OpenStreetMap. 14,997 of them worldwide, drawn as a dot sized by the area of the facility. At the closest zooms the dot is joined by the perimeter as it is mapped.

Click any facility to see what OpenStreetMap records about it — who runs it, and whether the state or a company operates it, where a mapper recorded that. Where it has a Wikipedia article, a short summary is fetched live and shown in your own language; and every facility links to the OpenStreetMap object it came from.

Mapped, not modelled

Each facility is an object a mapper drew, from survey, local knowledge or aerial imagery; nothing here is modelled or estimated.

One colour, and why

Every other layer on HueMaps colours its features by some property. This one does not, because OpenStreetMap does not record anything about a prison that could honestly carry a legend.

The only candidate is a tag saying who operates the facility, and it is on 9.5% of them — of which 86% say simply "government". Colouring by it would give one colour on about 8% of the map, a second on 1%, and grey on the remaining 90%: a legend that tells you nothing you could not have assumed. There is no capacity tag, no security-category tag worth the name, and no facility-type tag. So the layer is a single colour, which is the honest statement that this is a set of places and not a classification of them.

What the tags do say is shown on the individual facility instead, where a mapper recorded it.

Size

Each symbol is sized by the area of the mapped facility, in square metres measured on the globe. Symbol area is proportional to that (radius to its square root), so a facility four times the area draws twice as wide.

Prisons are usually mapped as their perimeter, so size here is close to a real measurement of the place — though it is ground covered, not population held. A low-rise facility spread over open country outsizes a taller one in a city holding more people.

Completeness — the strongest caveat on any layer here

OpenStreetMap is not equally complete anywhere, and for this subject the gaps are not only a matter of mapping effort. Prisons are politically sensitive in some countries; some facilities are deliberately absent from open data, some are mapped without being named, and mapping them is not risk-free everywhere.

So on this layer more than on any other, an empty area may mean the facilities are not recorded rather than not there — and the places where the record is likely to be thinnest are exactly the places a reader might most want to look at. Please do not read the density of this map as a measure of imprisonment.

A picture of the present

Today's map, not a history. OpenStreetMap is edited continuously; this copy is refreshed periodically. There is no year control, and a facility closed some time ago may still be mapped until a mapper updates it — as may one long since converted to something else.