I’ve seen many chedis in Thailand was tagged as a man_made=tower + tower:type=stupa. Taginfo shows that there are 1086 of this type of object around the world. I was searching for the origin and I found that it may have begun in 2013 by AlaskaDave’s edit of the wiki page https://wiki.openstreetmap.org/wiki/Key:tower:type (the page was separated from the man_made=tower page later), with the suggestion from cartinus (at https://help.openstreetmap.org/questions/20113/tagging-for-stupas-or-chedi ). What I’m not sure is why cartinus confidently said that “It’s a tower”.
Although a stupa is usually higher than its width, I’ve browsed through https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dtower and found that the difference between a man_made=tower and a man_made=mast is: “A tower is accessible and provides platforms, whereas a mast only offers ladder steps to climb it.”. By this message, a stupa should not be either a tower or a mast, as most of them are not accessible or have a ladder outside. Moreover, a stupa could be any height from only 1-2 meters to 100 meters. Tagging all of them with man_made=tower shoudn’t be appropriate. Some temple will consist of hundreds of towers, which is not make sense and would make the small stupa more important than it should. In addition, not all of the stupas are higher than their width, such as the Sanchi Stupa, the oldest stupa, is around 16 meters tall and 36 meters wide, while the Phra Pathom Chedi, the tallest stupa, is around 120 meters tall and 100 meters wide, not much different.
IMO, a tower or a mast should be something that provides a platform or any kind of function or purpose at the top, or nearly top, of the structure, as opposed to a stupa. A stupa is like a large sculpture used for worshiping. Most of them contains bone ashes or sacred items at their base or underground under them. So, the tagging of building=religious or initiating a new tag like building=stupa or even building=yes should be enough for tagging a stupa (with a whole temple area tagged as amenity=place_of_worship).
But how can we have a specific tag for a stupa? I suggest that is should be under the historic tag. Why?, because the stupa was built to commemorate something, mostly to bury bone ash (but some of them may not contain anything as they were built simultaneously to be just a symbolic structure for a temple layout). The similar kind of building I can think about is the Egyptian Pyramids, which are currently tagged as historic=monument. For the above reason, I can think of 2 ways of tagging:
- tag the main stupa of the temple, which stands out from the other buildings at its height, with historic=monument, and the general stupa in the temple with historic=memorial + memorial=stupa (create new one), this way can lead to a problem of deciding whether each stupa is a monument or a memorial.
- create a new tag like historic=stupa, this way is clear, but I’m not sure about putting a stupa in like a top-level historic tag.