Proposal:Tagging scheme for windmills and watermills

Tagging scheme for windmills and watermills
Proposal status:	Proposed (under way)
Proposed by:	AntMadeira
Applies to:	Applies to
Definition:	Differentiates building=windmill from man_made=windmill and creates the new key windmill=* to refine the use of both elements.
Rendered as:	picture
Draft started:	2025-01-27

Proposal

This proposal arises from the ambiguity between the tags building=windmill and man_made=windmill, whose wikis are almost indiscernible. The aim is to remove the association of the tag man_made=windmill to the building scheme, leaving building=windmill for those structures built as buildings to operate with the help of the wind (mostly to mill grains), and man_made=windmill to the devices which can operate independently or inside a building, thus clarifying the differences in their respective wikis. The same applies to building=watermill vs. man_made=watermill.

Rationale

As it happens today in OpenStreetMap, a windmill (normally mapped with the tag man_made=windmill) must be tagged with building=yes (or building=windmill or even building=industrial) to be correctly rendered in the map. Thus, it doesn’t make sense to have two tags to map a building when you can have only one, which fits perfectly into the building=* scheme.

After consulting the community in the forum, there were some ideas to try and solve this ambiguity and contribute to more logical and specific tags, which fits in the already existing schemes of building and man_made.

The main idea is to map windmills and watermills as buildings when the structures were clearly constructed with that purpose, and leave devices or apparatus included in the man_made=* tag. These devices can exist independently from buildings (see examples below) or mapped as the device inside the building (if it still exists). To specify the use of the windmill, this can be further refined with the the new proposed keys windmill:function=* and watermill:function=*.

As discussed in the forum, due to the fact that the word "windmill" is used in many places around the world as synonymous of various structures/buildings/devices, and in order to take advantaged of the more structured and refined definition of man_made=windmill, it is also proposed to deprecate man_made=windpump in favor of man_made=windmill + windmill:function=water_pump.

Wind turbines for energy production (also called "windmills" in some places) have their own well established scheme and will not be included in this proposal.

Tagging

The following tables includes tags/keys which will be altered, created or deprecated.

Useful combinations are also presented.

Altered

tag	description	examples	actual use
building=windmill	This tag would be used only for buildings purposely built as windmills, i.e., to harness the power of wind by means of blades or sails to mill grains (mostly), drain water, saw wood or other purposes. The windmill:structure=*, windmill:function=* and windmill:vanes=* keys can be added to better describe the structure and use of the building. The tag man_made=windmill should be maintained if the device still exist inside (see examples below). Preferably, man_made=windmill should be a node if the building is mapped as an area .		building=windmill $1% $1% $1% $1% More details at taginfo More details at taginfo
man_made=windmill	This tag should no longer make reference nor used to define buildings, since there's a more structured and appropriate tag for that. Instead, it should be used for devices with various purposes operated with wind energy. These can be external or internal devices. The present proposal suggests the transition of man_made=windpump tag to this one, deprecating the latter. The windmill:structure=*, windmill:function=* and windmill:vanes=* keys can be added to better describe the structure and use of the device. Pros: no longer use man_made=* to define buildings; the possibility to render windmills has buildings on the map, with their respective icon; reserve the more well known term "windmill" for those windmills which are not buildings and serve to pump water (currently man_made=windpump); introduce the key windmill:function=*, which can be expanded to refine the use of the device (pump water, cut wood, mill grain, etc.). Cons: For those windmill buildings already mapped using this tag, the tag building=windmill should be gradually added. For buildings in ruins, abandoned or disused, where the device is no longer present, this tag should be removed; The need to accommodate the migration of man_made=windpump to man_made=windmill (see below).		man_made=windmill $1% $1% $1% $1% More details at taginfo More details at taginfo
man_made=windpump	Since this element is considered a windmill, mainly in the USA and Australia, where they're more frequently used, this tag should be deprecated and migrated to man_made=windmill. It then can be further refined adding windmill:function=water_pump + windmill:structure=lattice_tower. A Maproulette challenge can be use to help in this task.		man_made=windpump $1% $1% $1% $1% More details at taginfo More details at taginfo
man_made=watermill	This tag should no longer make reference nor used to define buildings, since there's a more structured and appropriate tag for that. Instead, it should be used for devices with various purposes operated with water energy, be it inside or outside buildings. The proposed watermill:function=* tag can be added to define its use. Like with man_made=windmill, this tag should not be removed if the device still exists.		man_made=watermill $1% $1% $1% $1% More details at taginfo More details at taginfo
windmill:type=*	This key already exists and it's used to indicate the architectural/structural style, not the use. In the discussion page, it was proposed that due to its low usage, it could be adapted to a more descriptive key, one that can be better distinguished from windmill:function=*. The proposed key is windmill:structure=*. The existing wiki should be adapted to be used with building=windmill (because it is a structural description) and can have the following values (more can be added): post, tower, smock, tjasker, lattice_tower, roundhouse, etc.		windmill:type=* More details at taginfo More details at taginfo
windmill:vanes=*	This key already exists and it's used to indicate whether a windmill still has vanes (building or device). Its wiki should only be adapted and expanded to be used both with man_made=windmill and building=windmill and can have yes, no as values.		windmill:vanes=* More details at taginfo More details at taginfo

Created

tag	description	examples	actual use
building=watermill	This tag would be used only for buildings purposely built as watermills, i.e., to harness the power of water by means of wheels or other rotative devices to mill grains, fruits or to cut logs. To define its use, the proposed watermill:function=*and watermill:method=* keys can be added.		building=watermill $1% $1% $1% $1% More details at taginfo More details at taginfo
windmill:structure=*	As mentioned above, this key would be a migration from windmill:type=*, due to the ambiguity of the word "type", which could mean "type of building" or "type of use".
windmill:function=*	This tag is used to indicate the type of the windmill regarding its use, whether a building or a device. Possible values are windmill:function=water_pump, windmill:function=sawmill, windmill:function=grinder, etc. For the grinder value, the product can be further specified: product=flour product=olive_oil product=nut_oil product=ore product=bark_powder product=gunpowder etc.		windmill=* More details at taginfo More details at taginfo
watermill:function=*	Like with windmills, a watermill can be used to several purposes. Possible values are watermill:function=sawmill, watermill:function=water_pump, watermill:function=grinder, watermill:function=energy, etc. For the grinder value, the product can be further specified: product=flour product=olive_oil product=nut_oil product=ore product=bark_powder product=gunpowder etc.		watermill=* More details at taginfo More details at taginfo
watermill:method=*	Based on Watermill#Operation, there are various methods used in a watermill. This key would be used to distinguish between them. watermill:method=* *:method=water-storage *:method=run-of-the-river *:method=tide
man_made=water_wheel	This tag can be used to map water wheels outside watermills or in cases where the device is the only feature remaining. Based on Watermill#Operation, there are different kinds of water wheels. water_wheel=* water_wheel=undershot water_wheel=overshot water_wheel=pitchback water_wheel=breatshot		man_made=water_wheel $1% $1% $1% $1% More details at taginfo More details at taginfo

Deprecated

• man_made=windpump => man_made=windmill + windmill:function=water_pump
• windmill:type=* => windmill:structure=*

Additional tags

• material=* - the most common construction material of the building
• name=* - some historic buildings have their own name
• start_date=* - the date when the element was created
• craft=grinding_mill - typically mapped with a node , indicates if the windmill is in operation, with people regularly using it to grind cereals
• craft=sawmill - typically mapped with a node , indicates if the windmill is in operation, with people regularly using it to cut wood into timber
• ruins=yes - indicates if the building is in ruins
• tourism=museum - indicates if the building originally built to be a windmill/watermill is presently a museum
• tourism=guest_house - indicates if the building originally built to be a windmill is presently a guest house/chalet/etc.

Examples

type	example image	tagging	usage	description
Buildings		856992438 856992438 building=windmill man_made=windmill windmill:function=grinder product=flour windmill:structure=smock windmill:vanes=yes name=Upminster Windmill old_name=Abraham's Mill wikipedia=en:Upminster_Windmill website=https://www.upminsterwindmill.org/	or	A building built as a smock mill to grind grains. It still has vanes. The already existing tag man_made=windmill would be maintained, because the device still exists inside.
		building=windmill windmill:structure=tower windmill:function=grinder windmill:vanes=no ruins=yes	or	An old and ruined windmill without its vanes. There's no man_made=windmill any more, because the device no longer exists.
		building=windmill windmill:function=water_pump windmill:structure=tower windmill:vanes=yes material=wood	or	An operating wooden windmill which is used to pump water.
		298919173 298919173 building=windmill man_made=windmill windmill:function=sawmill windmill:structure=smock windmill:vanes=yes craft=sawmill name=De Salamander website=https://molendesalamander.nl/en/	or	A windmill building operating as sawmill, with reference to its type, to the existing vanes and the craft. The device man_made=windmill still exists inside.
		building=windmill windmill:structure=tower windmill:vanes=yes name=Moinho do Roque tourism=guest_house	or	An old windmill refurbished as a guest house. There's no man_made=windmill tag, because the device no longer exists.
		building=watermill watermill:function=grinder watermill:method=run-of-the-river name=Wrickton Watermill	or	A building built as a watermill operated by the running water of a stream.
Devices		man_made=windmill windmill:function=water_pump windmill:structure=lattice_tower		A windmill which is not a building, also known as windpump.
		man_made=windmill windmill:function=grinder		A wind operated mill.
		man_made=windmill windmill:function=water_pump windmill:structure=tjasker windmill:vanes=yes		A tjasker, a windmill device used to pump water.
		man_made=watermill watermill:function=grinder		A water operated mill device used to mill grain.
		man_made=water_wheel water_wheel=undershot		The water wheel of a watermill can also be mapped separately.

Rendering

The current icon for a windmill building would need to be attributed to building=windmill and not to man_made=windmill.

The icon for a watermill building could be something like this (used by HOT style):

Pages affected

• https://wiki.openstreetmap.org/wiki/Tag:building%3Dwindmill - specification of use and distinction from man_made=windmill
• https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dwindmill - specification of use and distinction from building=windmill, reference to the newly created keys windmill:function=* and windmill:structure=*
• https://wiki.openstreetmap.org/wiki/Tag:building%3Dwatermill - creation of page and specification of use and distinction from man_made=watermill
• https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dwater_wheel - creation of page and specification of type
• https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dwatermill - specification of use and distinction from building=watermill
• https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dwindpump - deprecation in favour of man_made=windmill + windmill:function=waterpump
• https://wiki.openstreetmap.org/wiki/Key:windmill - creation of new wiki page with mention to possible values as water_pump, sawmill, etc.
• https://wiki.openstreetmap.org/wiki/Key:watermill - creation of new wiki page with mention to possible values as grinder, sawmill, etc.
• https://wiki.openstreetmap.org/wiki/Key:man_made - adjust definition
• https://wiki.openstreetmap.org/wiki/Key:windmill:type - migration to windmill:structure=* and mention that the key should be applied to buildings
• https://wiki.openstreetmap.org/wiki/Key:windmill:vanes - change useful combination and mention that the key should be applied also to buildings

External discussions

The original discussion about this subject can be found at the community forum:

• https://community.openstreetmap.org/t/deprecate-man-made-windmill/107711

Comments

Please comment on the discussion page.

Community forum: https://community.openstreetmap.org/t/rfc-feature-proposal-tagging-scheme-for-windmills-and-watermills/125959

Tagging mailing list: https://lists.openstreetmap.org/pipermail/tagging/2025-February/068098.html