Watermills — how this layer is made

What you are looking at

Each dot is a watermill. There are more than 14,000 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=watermill`. A mill that still works as a mill and one that has been converted into a house, a restaurant or a museum all count, as long as a mapper kept the tag. Some converted mills are recorded only as the house or the restaurant, and those are absent. About three mills in five record a name.

Colour

There is one colour, because OpenStreetMap records nothing about a watermill that could support a legend. There is no well used tag for the type of mill, for what it ground, or for whether the wheel still turns. We would show whether a mill still works if the data allowed it, and it doesn't. Size represents the building instead.

The building, not the waterworks

This layer is the mill itself. Everything that drove it is mapped as a separate object in OpenStreetMap and is not on this map, including the weir, the leat, the mill pond and the wheel. A mill site whose building has gone but whose channel survives is usually not here at all, so the layer counts surviving mill buildings rather than places where a mill once stood.

Size

The size of a dot represents the footprint of the mill in square metres. Three mills in five are drawn as an outline, and among those a typical one covers about 120 m², which fits a wheel, a floor of millstones and usually somewhere for the miller to live. The remaining two in five are recorded as a single point with no shape, and we draw those at one nominal small size. At the top of the range are whole industrial and utility sites whose entire grounds have been tagged as a watermill, including a water plant at Kalyani in West Bengal, a flour mill in Burgundy and a set of livestock watering troughs in Kenya. 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

An empty area here means the mills were not recorded, not that none were built. Water mills were described by Vitruvius in the first century BC and were built for two thousand years across China, Persia, India, the Islamic world, Africa and the Americas, so there is no sense in which they were a European technology. What this map mostly shows is which mills survived as buildings into the age of heritage protection, and who has since taken the trouble to map them. In much of Europe old mills were conserved, converted or restored, while elsewhere they were replaced, rebuilt or fell down. It is a fair guess that watermills were once close to universal wherever water runs downhill and people needed to grind grain.

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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