Browsing through the issues at Openstreetmap-carto (also known as OSM Standard style or “Mapnik” style) tracker on GitHub, I came across several issues, both open and closed, touching the topic of rendering vertical man-made structures such as poles, masts, and towers.
Communication engineering was my thing for awhile, so it always strikes me when at least two of these terms - mast and tower - are used in an uncertain manner. In one of the discussions on GitHub, the difference between masts and towers was called “philosophical”. Actually, there is no philosophy (at least if you don’t look at wrong and misleading examples in OSM Wiki). Because of that, I’ve added an engineering definition to pages of
man_made=mast both in English and Russian because what is in the first section of those pages makes zero sense and contradicts the basic principles of tagging, because it uses comparative terms such as “bigger” and “smaller” to distinguish between these structures. Tags
tower:construction=guyed* are obviously redundant because if you need that, it means that object must be tagged as a mast, not as a tower.
I didn’t want to rewrite the whole “definition” without discussing it, while I don’t really believe that discussion could be successful, so I just added clear definition in case if someone would prefer it. Just for the reference:
Mast is a vertical man-made structure, supported by the guy lines and the anchoring system.
Tower is a vertical free-standing man-made structure, supported by its own foundation only.
(Anyone can find it even in Wikipedia, so it makes me wondering, how ignorant an author of these OSM Wiki articles was to write that.)
And it doesn’t matter, that some contractors (and regular people after them) calling cellular communication towers “masts”. It is not only wrong as it is to use “transistor” to call a radio receiver or “Xerox” to call a copy machine (which is common in some languages), but it makes it impossible to actually distinguish masts from towers for mapping purposes.
So, getting back to rendering, both “inverted T” and “inverted Y” are completely appropriate for tower symbols. Inverted T looks like a tower with a single stem or column, standing on its foundation,
tower:construction=freestanding. Inverted Y looks more like a rough outline of a steel lattice tower (more strokes could be added to make it look fancier),
Masts are a bit more tricky, but just a bit. The most obvious symbol is an “inverted bird foot” symbol, similar to inverted Y with the central stroke, extended all the way to the bottom. It also looks like an inverted antenna symbol used for circuit diagrams. Central stroke represents the mast itself, diagonal strokes represent guy lines.
As a bottom line, rendering of masts and towers is not solely a question of style and preferred icons, it’s also a question of using proper definitions. If definitions will get clarified one day, no philosophy will be involved in rendering and tagging anymore. (Personally, I really doubt that it will happen.)
Added from comments: These tags currently do not have “OSM-specific meaning”, they are completely mixed into one mess - it is technically impossible to be sure if an object, tagged with
man_made=mast is a mast and vice versa. So, changing anything can’t do any harm, because it can’t be messed up more than it currently is.
People are arguing about that only because almost every person has an own tradition of tagging and thinks that all others have a similar one. But it’s not true - different objects are tagged similarly by different people as well as similar objects are tagged differently by them. Belief, that there is any global consistency in tagging masts and towers is just a fallacy.