Windmills — how this layer is made

What you are looking at

Each dot is a windmill. There are more than 12,000 worldwide. There is only one colour, and the size of a dot represents the footprint of the building. Click on any of them to see what OpenStreetMap records, such as who looks after the mill and its website. 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 mill 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 mills.

What we include

We use one exact tag, `man_made=windmill`. A mill that has lost its sails or has been converted into a house may or may not keep that tag, and the practice varies from mapper to mapper and from country to country. About four mills in ten record a name, so many of these dots tell you only that a windmill stands there.

Colour

There is one colour, and that is a decision rather than something we forgot. The tempting division is the type of mill, since a tower mill, a smock mill and a post mill are genuinely different buildings. Fewer than one mill in ten records its type, so nine dots in ten would be grey. The vocabulary is also north-west European, and it has no term for the windmills of La Mancha or for the vertical-axis asbad of eastern Iran, which is very probably where the technology began. Size represents the building instead.

Not wind turbines

This is the older meaning of the word, a building that grinds, saws or pumps using sails turned by the wind. A modern wind turbine is a different thing, it is tagged differently in OpenStreetMap, and it is not on this map. There are hundreds of thousands of turbines worldwide, and putting them here would swamp the mills entirely.

Size

The size of a dot represents the footprint of the mill in square metres. About half the mills are drawn as an outline, and among those a typical one covers about 40 m², which is roughly the base of a modest tower. The other half are recorded as a single point with no shape, and we draw those at one nominal small size, so for half this map the size is not telling you how large the mill is. Footprint still works as a measure, because a great Dutch tower mill really does cover several times the ground of a small post mill. A few of the largest features are industrial flour and rice mills whose whole site has been tagged as a windmill, and they draw far larger than any real mill. We cap the size scale below them and leave them in, because no rule that removed them would spare a genuine mill complex.

Where the map is empty

Most of the blank on this map is real. The windmill as a building was developed and built at scale in the Low Countries, England, northern Germany, Denmark, Iberia and the Aegean over several centuries, and it was never the technology of choice across most of South and East Asia. An empty area here is usually a place that never had many windmills rather than a place nobody has mapped, which is unusual on this site and worth saying plainly. Within the mill-building regions the ordinary caveat still applies, and how thick the dots look depends partly on how thoroughly each area has been surveyed.

Up to date, mostly

OpenStreetMap is edited continuously, and we take a new copy once every one to three months. A mill demolished some time ago may still be mapped until a mapper updates it.

Source and licence

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